Anger frequently comes from feeling that someone did not treat you with the proper respect. People tend to feel angry with someone who fails to show them the honor they think they deserve.
The solution is to contemplate how valueless honor really is.
When you react to slights to your honor with a sense of personal dignity, you gain much more than when you lose your temper. The greater your own realization that you have intrinsic worth since you are created in the image of the Almighty, the less the slights of mortals will affect you.
Sources: Maaneh Rach, Ch.6; Rabbi Zelig Pliskin’s Gateway to Happiness, p. 196