Any tips for someone who has to keep their cool while dealing face to face with someone out to destroy them?

I know, I know this question sounds paranoid but… My ex is still quite furious that we are no longer together. Tomorrow we meet face-to-face to try to hash out some important issues. I know he will come loaded for bear and I am determined to keep my cool no matter what. I have some ideas of my own for staying calm, but I would love hear some thoughts from my fellow jellies.