When a driver tries to let me go in front of them at a stop sign or when I am in the lane, stopped and signaling a left turn and an oncoming driver stops on the highway to let me turn left, I generally take both feet out of the pedals, hands off the bars, and make it clear that I am not going. Once it was someone I sort of know, and when they complained to me about it I told them that the usual rule is "everyone wants to kill you on your bike, trust no one". To the guys credit he was flabbergasted that I would think that way.

One good thing about threads like this is that not all of these urban situations apply to me where I am, but its good to know about them when I ride in a city.