I was angry as hell at the end of my drinking career, and I have known a lot of miserable drunks, and the world has seen plenty of out of control behavior by drunks, so I vote for booze as the most anger-producing.
The prohibition of it is unfair and illogical, so maybe it provokes because it is so fucking stupid
I use pot to medicate instead of upping my Prozac or trying another "cocktail" that the psychopharm suggests. Pot enables me to cut way back on those meds and function just fine. I have depression and I don't want more of those drugs. If something natural works, how lame is it that it cannot be used...that is the frustration.
In lines or traffic I practice releasing the anger because it feels so toxic. Of course, I do that after I have already spent a minute or two cursing and railing!!! I am just a fast walking, fast thinking and talking person who will always have to work at reining in the tendency to force the pace of life.

But with regard to other people, I think I am getting better.
I am learning to "suffer fools" a bit more because I have to do that with students (or they would all cry) and also I am older- I used to be much more impulsive.