I have only "hit" a car once - two years ago I caught up to a car that buzzed me...actually felt the mirror hit my jacket...knocked on the passenger window and yelled at the driver (young girl who was obviously scared) to give me more room next time.

I got cut-off earlier this year, and caught the car at the next red light where I squirted the drivers window with my water bottle to signal my displeasure. Last year I got cutoff (at the exact same spot) and caught up to the guy at the next red light. I yelled at him to give me room and he responded by flipping me the bird. It was raining pretty good that day so I reached over and flipped up his passenger side windshield wiper such that he would have to get out of his car and flip it back down. I feel a little bad about the first two incidents, but I am still feeling pretty good about the last one.