They say depression is anger turned inward, and I think that is true. So when I see someone who is angry a lot, I see it as their defense (coping) mechanism and it serves a purpose. Striking out or blaming others can prevent one from becoming so depressed and maybe even suicidal. I learned that about myself since having PTSD. I just think that it needs addressed for anyone who suffers this, and I suffer this too, but mostly at myself.
Then there are times that I am angry at someone close to me, which often comes from frustration. I think we get angry for different reasons (hurt, insecurity, jealousy, frustration, etc) but many times have a theme to that anger. My theme seems to be frustration. I seem to have people in my life that have not communicated well or don't do what they say they are going to do, so its usually rooted in frustration. When I listen to their point, it can de-escalate it, but if that other person just repeatedly makes excuses....gonna get same result.