The Bible tells us in the Epistle of James, to be quick to listen, to be slow to become angry, and to be slow to speak. Any time you feel that you start to get angry, stop, take a pause, do not talk for a few seconds or if possible minutes, until you feel calm, then talk, regardless to whom you talk, or what you talk about. That will give your brain, to respond logically, thoughtfully to an event, instead responding out of emotion, which possibly you will regret latter. We tend to respond out of emotion much quicker, than out of logic and thought, to events which bring us stress.
If you have build up stressful negative emotions in yourself, admit to yourself that you feel angry, and say to yourself, I feel angry because of this or that, and try to feel for yourself, that angry feelings. Accept them for yourself, and do not pretend that you do not feel angry, because that will increase anger. The way to diffuse anger, is to accept for ourselves, that we feel angry, feel the anger ourselves. You can write your angry feelings on a peace of paper, and then tear up the paper afterwards.