I learned many, many years ago, as a astudent, when I had to pick up my bike and turn it around to ride the other way when someone got out of a car after me, (I had returned the middle finger greeting) that the best thing to do with an irate driver is to pretend to be so stupid you think they are being nice and friendly. I always stupidly smile and wave. They give up if they think you are too stupid to even insult.