I feel bad for days when I respond with obscenities to a driver that deserves it. So now I smile and wave and say Hi! in response to anything shouted at me. Responses are so funny most of the time that it makes it all worthwhile.

If someone physically threatens me with their vehicle, I'll call the police. Screaming at me is not worth the trouble. But this really only works when you follow the smile and wave routine. You really have to prepare yourself for it, otherwise you'll revert to old habits.