I just had this sort of thing happen recently. had an agressive(young) guy and his buddy come up behind me at 40mph and honk as they got behind me and went around me. no reason to honk. so I just raised my hand in a "Why as that necessary" gesture, and they both flipped me off. The got stuck at the next light and as I rode up behind them, I grabbed my phone and pretended to be on the phone with the police speaking VERY loudly so they could here me giving the make/model of the car, and the license plate, and explaining that they tried to run me off the road while honking at me while no other cars were around. all people in the car started looking around, as I explained to the fictitious officer where we were and the direction we were traveling. Shut them up pretty quickly.