Engaging a road rage idiot is giving them just what they're looking for with their behavior. They don't get anything more than a blank stare from me, with handguns everywhere it's the prudent thing to do.
I go the blank state route too, seems to communicate “I might have a firearm that I don’t want to use but I will if I have to” pretty well, or maybe they think I’m just a lobotomy patient I dunno.
Either way, it seems to work.