What do you do to calm down when mad?

Take some deep breaths and think rationally about the situation. I think about how I would navigate the situation were I to be calm. Another thing I do pretty frequently is think about how important/impactful the situation actually is. Ten years down the road, am I going to be thinking about the situation I'm currently in?

If it's not something I'm going to carry with me for the rest of my life, why waste my time being upset about it?