I encountered one of those yesterday. A driver stopping in traffic and waiting for me to go when I couldn't because of traffic in the other direction. I worry that all the drivers behind the guy who stopped needlessly will be upset at cyclists for slowing traffic. Or they could try to pass the stopped car and create a more hazardous situation. I'd rather wait for a break in traffic than depend on driver B to guess what driver A is doing.

Then there was the time I was riding straight down a road where a policeman was stationed to help cars turn left into a school driveway. The policeman motioned for a car to turn left right in front of me. The driver saw me and refused to do so, while the policeman began to get angry with him. You don't expect a policeman to totally not see you and almost cause an accident.