There's no point in getting mad. I am going to breathe deeply and relax. Take some time. To calm down right away, count to 10 or take deep breaths. When there is more time, talk about your feelings with someone not involved, listen to music, exercise, write to the person explaining how angry you are and then destroy the letter, help someone, watch a funny movie, work on a hobby, have a good cry, yell at the top of your lungs where no one can hear you, or spend time with a pet.
Anger is normal.
Decide whether you can change the situation. If not, let it go. Give up unrealistic expectations for yourself or others. Remind yourself that others have the right to think, act, and be who they are. Act in ways that will improve the situation.