Yes, people get angry. Even you and me. Anger can be triggered by someone being mean, being a bully, or by someone belittling us. It comes from a feeling of injustice or imbalance.
We feel ANGRY because we feel life is unfair,"they" get special treatment, "they" are lucky, or special, and the list goes on. Really, we get angry because our Ego jumps in and says we have been wronged.
We need to let anger go. It is difficult. However you would like to release anger, begin with, "I release the anger, resentment and regrets….", and your world will be changed.