I have an ENTP friend that gets pissed if I don't answer my phone... which is all the time, and gets even more pissed if he thinks I answered because of my deceptive answering machine, and he'll precede with a five minute cursing session of total nonsense to rant. He gets over it instantly, I mean after he finishes the ranting. But, laid back as long as nothing is getting in his way, he'll walk around but he'll rant the entire time. Really one of the quickest tempers I've ever known, but never out of control at least. But... ENTP from my experience doesn't seem that laid-back, way too many pet peeves that come out of nowhere.
If I knew another INTP... I'd say INTP would be among the most laid-back, but I only have myself to go off of. I think I've seen people get pissed off/annoyed within a month of knowing them than I can even remember myself even giving a second thought about any of these things I see them annoyed about.
Too many grey areas in my perception, everything is trivial to me, need more information, so I don't bother wasting my thoughts on developing opinions unless it somehow instantaneously develops, in which case I'll try to figure out where that came from, and before I figure it out, time has passed, not even worth worrying about anymore. Dismissed, forgotten.
The ENFP I know, lazy, but... laidback? hell no, anything goes against what he wants he's capable of throwing a fit, and won't even be angry, he has fun doing it. Also will find any excuse not to do a chore that is out of his way, unless he feels like being nice or feels like he owes you.
The IxFP I know... has mood fluctuations ever since I've known her, and will be happy, than suddenly angry, more like withdrawn I'm not talking to anybody angry and stomp around the place, but yeah, I don't see laid-back in that behavior.
Of course, people are different, just my experience, not egg shelling anyone, just observations.