Try this one:
You are driving north behind Mr./Ms. Politeness, who slams on his/her brakes for no apparent reason, simply to allow someone stopped in the southbound lane to make a left turn in front of them. This is maddening in the extreme. Mr./Ms. Politeness has just caused an untold number of cars behind them to come to a full stop, all for one driver who was already stopped.
Worse, this polite behavior can be dangerous. I watched a driver do this about six months ago, insisting by hand signals that the stopped car make a turn in front of them. Unfortunately, there were two northbound lanes. The southbound car made their turn in front of Mr./Ms. Politeness, only to get t-boned by a car in the other northbound lane. Of course, they could not see this car, with Mr./Ms. Politeness stopped in the way.
IMHO, things are safer when drivers behave predictably. Predictable behavior includes NOT ARBITRARILY STOPPING WHEN YOU HAVE THE RIGHT-OF-WAY.