Every cyclist regularly meets seriously rude drivers. Faced with a driver honking, screaming, or cursing at me, I have two bad choices: I can say, and do, nothing, and give them the impression that I agree they have no obligation to share the road with me, or I can use the one gesture universally recognized in traffic. Unfortunately, that one gesture does more than ask a driver to back off, or reconsider their actions. It communicates hostility, disrespect, and aggression.
We need a gesture that tells the driver we think he or she should smarten up, pay attention to the road, and stop honking or cursing at us for doing things drivers on four wheels do all the time. But we need a way to communicate that without getting aggressive or nasty, and escalating tempers further.