Have you ever been angered before?
This question sounds strange to me; are there people who have never been angered? I wanna swap lives with them!
Why?
It usually has to do with someone crossing a line that I've deemed uncrossable, something that would make me go basically "oh no you didn't!" and then explain to them exactly why I don't like what they're doing. Over time, I'm caring less and less about stuff and letting more things slide, and these "uncrossable moral lines" are disappearing as I become apathetic. One small bad thing after another really adds up though and that can cause me to be angry or irritable too.
What was it like?
I'll explain here how I felt: At the very worst, I will be shaking, incoherent, and the anger will take over my ability to think well enough to even form sentences. I really hate that because during those times when I'm mad, more than ever, I want to change something about the current situation, which is much more difficult when I can't even think straight. More mild anger has a similar effect but to a lesser degree; it'll hinder my ability to think logically and objectively unless something is done. Not being able to think is a scary thing for me because I spend all of my time thinking.
How will INTJs show anger? How do you do it?
If somebody has done, said etc something that offends me a lot or I think is very wrong, the anger may come out in a long explanation of why I think they're wrong (which is usually incoherent as I said above, and I realise this so I avoid it). This explanation is an extreme way of "doing something" about the problem. Usually I either avoid the person/problem, or just make a sarcastic remark or some comment, and it doesn't even matter if they don't hear or understand because it satisfies my need to do something (note that doing something != changing things or making a difference, just pleasing myself sufficiently so I can stop thinking about it). If I'm just having a bad day, and it's more of a buildup of small things rather than a specific thing, I'll do something to escape like listen to music or (over)indulge in something that pleases me. During this time when I try to calm down, nobody can interfere in any way and I will do everything to escape from the current situation which is causing me anger or stress. Leave me alone, give me my 15 minutes. If I can't have that then I'm not a fun person to be around; I unapologetically speak any negative thoughts on my mind eg I might flat-out say things like "I don't care" if someone's being uninteresting. I get into this mode where I stop giving a damn about anyone or anything. Things I'd normally think are important become things I don't feel bad about neglecting. As soon as I get my 15 minutes though, I'll be okay.
It really helps if there's someone who I can complain to about anything. My best friend is like this and it helps me deal with things that would normally occupy my mind all day. Remember how I said I must do something or I'll regret it? Something as small as ranting to him is enough to make me feel like I've done something, and that thing will no longer bother me.
How long did it lasted? Did you regret it?
It lasts until I do something and I regret doing nothing

There are still things, tiny things that everyone else has forgotten about from years ago, that I'm pretty mad about to this day :/ But there's nothing I can do about the past so I just avoid thinking about it. I regret when I was younger, I had more "uncrossable lines" in my head, and I got mad more frequently and more intensely. I would react in ways that not only were extreme, but also didn't fix the problem. I'd yell a lot and would let basically nothing slide, and was not happy with anything less than what I deemed a perfect (looking back, usually unreasonable/impractical) solution. Over time I learned that you catch more flies with honey than vinegar and that staying calm and being patient is more effective. I've also learned that some battles aren't worth fighting. So I regret those times when I was more sensitive and easily triggered but I think I learned from them.
Hope I didn't forget anything important >_<