When showing up is a must, I try to work at calming myself before the event with deep breathing excersises. Then I try to stick to myself and keep my mouth closed(as this is one of my big problems) and remind myself I'm there for the comfort of someone I love(used to go to a family dinner for my dad's sake, where arguing was considered a fun past time.)

Try to stay calm and separate from the drama. Not easy, I know but it's about the best that you can do. Sit back and just observe. Sometimes it can be fun to look for the humor in such a situation.

Good luck.