To prevent myself from saying something I may regret, I pinch my ear. Or rather, I place my index finger and thumb on the front and back of my ear stud and press tightly. Not hard enough to draw blood, but just enough to leave a sharp pinprick indentation in my thumb. I don't think anyone around me thinks this is anything but an absentminded gesture. They don't realise this is the only move that saves my sanity right there and then.