Anger is complex, as it can be a response to many underlying emotions. I have struggled with inappropriate anger in the past few years, as I never learned to express the underlying emotions properly. For me, anger was the expression of fear, hurt, abandonment, betrayal, pain, distrust, etc. Having grown up in an abusive home where expressing any negative emotion was to put yourself at risk and then finding this same pattern in an abusive marriage, I honestly never learned how to express negative emotion in a healthy manner.
The there was one day that it just all came out, or should I say, came in. All of the fear, hurt, betrayal, pain, etc. came flooding in and I was angry, so very angry at myself. Then it just all spilled out to those around me. It felt so bad, out of control and poisoness that it developed into so much self hate that I ended up very suicidal.
It is OK to feel the emotions, including anger, and there is nothing inherently wrong in that. How that emotion is expressed is critical, as no one has the right to attack another person. Inappropriate anger expression isn't always "in your face" as it can be expressed through sarcasm, passive aggressive behaviors, avoidance, etc.
Learning to process and express emotion properly is tricky, and I am working on learning to be assertive, without being a doormat or being aggressive. I find that when I have been in doormat mode for a while, something trips me and I come out swinging. Some things can just roll off, but other things need to be addressed and when I bottle them up, the pressure builds and the explosion happens.
I just have to keep reminding myself that I have choices and it is up to me to make the choices and control my responses. No one can "make" me anything, and knowing that I have control helps me to make better decisions and have more healthy responses.