This is a great question, and one that I'm still learning. Matter of fact, I had an outburst this morning when a bus driver wouldn't let me board his bus with my service animal. Suffice it to say, I was yelling and making a scene in front of everyone, threatening his job. I'm embarrassed about my behavior.
What I've come to learn about my outbursts, is that there's some small part of me that feels invalidated and threatened. When I feel invalidated I can sometimes feel threatened, and when I feel threatened I become angry.
It's gotten a lot better since I started practicing just being aware of the anger. I slowly became aware that it was covering up other, more painful feelings; fear and pain. When I feel fear or pain, I can get angry.
Wish I could just tackle this monster once and for all. It has no use in my life.
Hope this was helpful.