I completely and categorically agree with you - NEVER make decisions when you are angry.
Decisions should be made with a level-head, must be objective and without bias.
I too walk away and cool off whenever I sense a negative situation building up. I keep calm and strong but I don't blow up and make scene. I walk for about 10 minutes or so and then return and conduct myself like a gentleman.
Also it's worth pointing out that revenge is a waste of time. If you have let someone upset you (because you are in control of your own emotions) it's a big waste of time thinking of ways to get revenge on that person(s). A much better strategy is to think positive and make progress and put your time and energy into become a very successful person in life.