Heard a story at a LBS about a guy who had a coke can thrown at him. Turned out he was a good racer and caught the guy at a light, reach in the car and punched the dude three time. The story goes that most of the other cars who say it were clapping for the biker. I do not condone that action. I remained calmer than I thought I would and just let law enforcement handle it. Another guy said the couriers carry bolts and either throw back or bust the window when they catch a car. It's more stressful to get even than just letting KARMA handle it.