My boyfriend had an encounter the other day. After being yelled at as the driver passed him they were both stopped at a stop light. My boyfriend got spit on, he retaliated by leaning towards the car to yell at the driver. The driver grabbed him by his shirt and his leather cord necklace. The BF retaliated by trying to punch the driver through the window and kicking off his rearview mirror. The fight continued to escalate into wrestling on the ground. Finally bystanders threatened to call the police and the driver got in his car and left.
I am not saying that he handled this appropriately or not. (He used to be a bike messenger in a big city so he seems used to this type of confrontation.) I don't know how I would have handled it. I probably would have just rode away as quick as possible and then cried most of the day. I'm thinking the mace might be good.