AHA so I'm not the only one who just shrugs when I get pissy >.>;;
Still there are a few issues here, and one of the foremost is yeur automatic assumption that he's broken and needs to be 'fixed'.
Now, going by whot yeu've said, I'd assume that for the most part this isn't a big deal, except for when it immediately affects work. The biggest thing to realize though, is that an ENTP generally will need time alone doing something they enjoy to distract themselves. Rarely do they hold a grudge for any length of time, but it will last indefinately until they can get their mind off it. Trying to force the matter will NOT work EVER.
I'll use myself as an example, as it's always the easiest way to do things XD
Personally, if I get upset over something, I will maintain my frustration at it for an infinite period of time, until either A: I manage to confront it head on and proove myself its' better, or B: distract myself long enough with something else that I stop thinking about it. The biggest problem, is that trying to distract oneself when something's gnawing at yeu, is difficult... just 'forgetting' it for a few minutes isn't enough, because the second something jogs yeur memory, yeu're back on it and frustrated again. The frustration usually lasts a few hours and there's really absolutely nothing anyone can do. Any interaction with anyone will inevitably lead to them trying to help on the subject, or getting annoyed that the ENTP isn't being very friendly at the moment or just leaving. Any and all of these are terrible resolutions, as going "oh well guess yeu don't want to talk, I'll see yeu later" is immediately viewed as abandonment, any call on being in a bad mood just reminds them to the reason for the bad mood and reaffirms it, and anything which involves trying to change things will be met with digging their heels in and being obstinate about it out of spite because they're probably already annoyed that someone didn't value their opinion, directly translating into belief they didn't care for the individual themselves.
Obviously, this isn't the case, but hei, we're not talking about common sense, it's an emotional thing, of which ENTP's generally aren't great with anyway, which only complicates matters.
The only thing I've ever found to work for myself is to watch 'intelligent' tv(really, it exists... sort of...), or play a game, or SOMETHING, the worst possible thing to do is to do something yeu don't enjoy, or try to relax. It won't work. It has to engage the mind fully and focus all my attention upon it, until I'm practically in a trancelike state for putting so much thought and focus on the idea. This more or less seems to clear the slate by removing all thought from the previous issue and directing the hostile energy elsewhere, pouring all effort into the current situation.
If for any reason, this's interrupted at all, before complete focus has been achieved, then it has to be started all over again from scratch, since the mind'll immediately jump back to whot was causing the problem in the first place.
Now then... the direct questions.
1) Does this sound familiar?
Not in that exact way, but yes very familiar.
2) how can we get him to relax the defensive barrier once built?
This's a bit more complex than yeu'd think... it's not a standard defensive barrier that lasts until it's broken down. It's a nigh-indestructable short term wall, it can NOT be damaged externally no matter whot anyone tries. Any attempt to prod, poke, or help will only reinforce it, making it take longer to be removed. Yeu can NOT interfere with it.
Likewise, this isn't an infinitely existing barrier either... it can be removed quite easily, but it must be done by getting the individual to focus their attention fully on something they want to do; the barrier is held togeather by their own sense of spite and annoyance, as soon as their attention is elsewhere, it weakens. When 100% of their attention is busy on another topic, it's gone, and nothing left. If yeu direct them to do something though, there'll be a slight taken to it, and it'll never be a true 100% attention... yeu may be able to get 90%, but as long as 10% of their attention is focused on their annoyance that yeu told them to do it, they'll never truly get involved into it to the point that it clears the wall. Even if this imaginary wall is knocked to the foundation, as long as there's even a few crumbled rocks left, the second they glance back at it, it rises back to full strength immediately. The only way to kill it is to have it gone entirely. That means no interruptions, no emails, no checking up on them, and no interaction of any sort which will draw their attention away from whotever it is they're doing.
On the other hand, this also requires that the ENTP will need to know that this is pretty much the only cure (at least the only one I've ever found, and trust me I've TRIED). They need to recognize this for themselves, because it's something they themselves have to initiate and do. If yeu try to trick them into doing it, it'll only cause it to backfire every time. I know yeu want to help, but anything yeu say and do only furthers the problem.
Fortunately, this's a rather useful thing as well... as soon as yeur problematic ENTP knows of this issue, and the resolution, it works pretty much every time consistantly and reliably. Yeu will only ever have to discuss this with them ONCE. Yeu will, however, have to do so at a time when it's not bothering them, because they won't listen when they're upset. If yeu can catch them at a time that they're in a good mood, or even better, in a debating mood, yeu can get them to explore this as an option. Once they know whot they have to do and take it to heart, they can initiate the issue on their own side. Then it's just a matter of when they get pissy, to leave them alone for a few hours, and they'll be fine after they're done.
In short though, this will require one major component: uninterrupted peace, from EVERYTHING. If they have to eat, go to the washroom, perform any mandatory tasks, or anything that interrupts them, they'll have to start over from scratch basically. Make sure they know to take care of everything before they begin. Then, make sure there's something they WANT to do that will take 100% of their attention to do. They'll probably need a fair bit of time in this focused state, roughly about an hour. The trouble is getting to the focused state in the first place, and then maintaining it without interruption. As such, the cure generally takes 5-6 hours on average, sometimes it's quicker, sometimes it can last overnight, though that's fairly rare.
In short though, once yeu get the shrug, they have got to be left to their own devices, as anything that draws their attention to the original problem, even anything as simple as an appology, will only cause problems.
3) How can we avoid provoking the defensive response?
Well yeu can't avoid it100%... ENTP's have a nasty habit of being able to cross referance many complex things at a time, meaning even several innocent statements on their own can be combined in a way that wasn't intended, and there's really no way to stop it at that point. Closest thing yeu can do is avoid directly confronting them or telling them they're wrong. If yeu have to make them understand they made a mistake, get them to go through the process of working through it themselves a piece at a time, with guidance. If yeu want to show them they're mistaken, it's alright to say "I think yeu're mistaken", because that's not a direct attack, it just means they're going to go into a mode where they'll be spending all their energies on prooving yeu wrong. The trick is to make sure that yeu just say "I THINK yeu're mistaken", and then walk them through the explaination, making sure they do most of the reasoning work, and nudging them down the correct path when neccesary. Keep in mind, they're going to be merciless in their evaluation in attempting to disproove yeur belief, so unless yeu know the topic inside out, yeu're probably just going to reaffirm they were right in the first place. Yeu will have to objectively proove every single thing they thought was correct is not, and make sure there's no room for error, as well as ensure that they do most of the thinking on the matter. If they realize they're wrong, they'll generally accept it and just change their opinion, but they're not going to just accept a "I think yeu're wrong" and change their mind on a whim, yeu need to proove it.
If yeu have anyone who can do that for them, it'll prevent the vast number of problems.
4) Can he be taught alternate ways of responding, that are less destructive to teamwork and communication?
Not really, no.
This's again based upon my own self, but personally, I've learned that even IF I know for a fact, that I myself am being unreasonable... it honestly doesn't matter. It's odd that way... I can KNOW that I'm being unreasonable, or obstinate, that I'm clearly not thinking straight, or being in a sulky pissy mood for no reason, but there's really nothing I can do about it. I can't just magically turn the switch off, and even with the realization that it's occuring, it doesn't actually seem to translate into actually doing anything to help the matter.
Don't ask me why, I haven't quite figured that part out yet, I just know that it IS. I'm still working on the WHY it is part. But if this's not a personal quirk, and is maintained by most ENTP's, of which seems likely considering anything I've read, chances are there's pretty much nil that yeu can do to change the behaviour. Yeu can limit its' occurance, and speed the recovery process, but yeu can't stop the actual 'shrug' as yeu put it. It's a natural reaction to certain stimuli; it's like trying to teach someone to not pull their hand away when they touch a hot stove... it's exceedingly rare that it's even possible to do it, and in the rare situation that it's possible to train them to repress the natural reaction, it didn't solve anything and it just made things worse. If yeu somehow DID manage to prevent this reaction, yeu'd probably be stuck with them either bottling it up and causing far more problems than before, or it'll just be expressed in another manner which could be either more destructive, and/or more difficult to contain and correct.
At the moment, yeu are dealing with a symptomn to a problem. Yeu can either A: reduce the chances of the problem occuring, which directly prevents the symptomn from showing in the first place, or B: deal with the symptomn when it occurs in the most efficent manner possible.
As this's a reaction to feeling slighted usually, or being accused of something they don't believe in, yeur best bet is to limit those occurances by handling the individual differently, which'll reduce the number of cases. Once a case does occur, it's their reaction to whot happened, and they ARE going to react regardless of whot yeu do, but this is their natural way which will deal with the problem the best way for them. If yeu do manage to change their method of displaying their frustration, it'll probably just make it more difficult to deal with because it's not their natural response any longer, so the treatment will have less effect, as it won't feel to them like they've truly fixed the problem. It'll keep nagging at them, or take far longer to correct, because it's not handling the base problem (the original frustration) in a way that feels to them like they've actually removed it.
Though... in this case it's kind of weird because the solution doesn't actually involve handling the problem >.>
There is the second method I mentioned though... but it's very very very risky, so I advise against it because it has an exceptionally high chance of just making things far worse.
This's that if there's something that directly caused them to get annoyed, or make them feel like they were slighted, or accused of being wrong... they can directly challange it head on, and tackle it with all their effort focused on prooving themselves right. This can, and will backfire if they actually AREN'T right. If they're wrong, then this's the last thing yeu want them to do as it'll just proove they had every right to get that way and it'll just make it even harder to pull them out of it.
If they're right, it works very well and quickly negates the problem usually. But they have to be right for it to work.
If they aren't, yeu're stuck with the other method of letting them cool off and diverting their attention. Once that happens, they'll no longer be upset, and will be able to clearly think and handle the situation calmly once more. Until they're in that state though, it's near pointless to even bother trying to get them to tackle the actual problem that's concerning them because they won't be able to think clearly on the matter. Once they have themselves balanced, and able to work on it, they can generally accept the problem for whot it is, without getting frustrated on it, and just work on solving it.
As such, the 'cure' to the 'sigh' is twofold...
A: if they're right and are just insulted in their own way, forcing them to proove they're right will immediately cure it. If it's impossible to proove, or they are in fact not correct, it'll just make matters worse.
B: if they're incorrect or unable to realistically proove themselves, then yeur best bet is to let them be for awhile, so they can calm down. Once they've broken their wall down on their own, which generally doesn't take long if allowed to do so without interruption, then they'll be fit to actually tackle the problem. They will be useless to yeu as long as they're stuck in the sigh mood, and will not be capable of handling it, or anyone else, until after.
I think I've ranted long enough... also note that this's mostly from personal experience, and there MAY be alternatives to which I'm not aware yet. I'll be doublechecking the replies here to make sure I didn't miss anything that could help me as well, for obvious reasons XD
Most of the time though i've found that it's not too hard to get me knocked out of the 'bleh' mood as I've put it, more than a 'sigh', though it often does involve sighing... it's just a pain to do if there's any interruptions. I know for a fact that anything I don't want to do (doing dishes, cleaning, anything like that) will have no effect, and anyone trying to help isn't able to, even if they attempt to give me something to do with the express intention of trying to get my mind off things, if it's not something I myself chose it won't work. The only way I've ever broken out of it, was to do something like eat so I'm not hungry and distracted while doing it, and then give myself some sort of puzzle to occupy myself with until I become so absorbed in it, I loose track of whot it was I was upset about. Oddly enough, once I'm done, I'll still know whot it was that annoyed me in the first place, but I just won't care anymore and won't be so frustrated over it. I hope fully that this entp of yeurs works the same way.
And yes, I know that normally ENTP's deal with problems externally through other people, but this's about the one case where they fall inwards on themselves. Once that's broken, they tend to return to normal.