I'll try.
It seems to me that most of my anger (which isn't very often) comes about whenever I'm not really in control of the things or people around me. It's like a survival/self-defense mechanism...the biological differences are obvious when you become angry. It's simply a matter of feeling uncomfortable (which to me...is when I feel like I'm not in control).
Your original post appears to be based on a specific thing that happened to you (although, I could be wrong). I can only assume that someone that you liked/trusted did something to you or reacted to you in a way that you didn't expect and didn't like, so you are reacting with anger.
I used to get angry a lot...now I pretty much only get angry when someone disrespects/embarrasses me. Let's say (hypothetically, of course) that I bare-knuckle boxed a couple of years ago. When I realized that it really wasn't all that bad, I started to feel far more comfortable everywhere. I wasn't afraid to fight because I wasn't afraid to lose and I knew that the chances of losing were slim anyways because I'm willing to do anything for myself and those that are important to me. As an INTP, I'm sure you can identify with at least part of that.
I saw a quote once that said something to the extent of, "Yea, though I walk through the valley of the shadow of death, I will fear no evil, because I am the evilest mother fucker that ever walked through the valley."
Does any of that help you? Maybe not, but that's my thoughts on anger. Standing up for yourself isn't just about being physical. It can be emotional too. If you don't feel comfortable opening up to people, let them know that. If they can't accept it, that's their problem. If you don't like people dumping their emotional baggage on you, stop listening. I've got more examples if you don't understand entirely where I am coming from.
I understand where you are coming from. And I do agree with staying away from people who are draining and controlling. Your insight has helped me delve into the problem a lot deeper. Sometimes, I feel so blind to my own motivations. Maybe human contact is good for these sort of issues.