A close second to this cul-de-sac pet-peeve is when folks park going the "wrong way" on a street, because they are (presumably) too lazy to turn around prior to parking. There is a safety factor to this; it is safer for them to exit their vehicle on the "curb" side and not in traffic. But ... There is a safety factor for the public that counters the driver's issue. When approaching a vehicle that is parked "wrong way" on your side, it can confuse someone in short duration as to making them believe they are not on the "right" side of the road, or going the "wrong way" down a one-way street. This is confounded at night when it's more difficult to ascertain markers and delineations.
And then they're the idiots that want to waive their right-of-way to be "kind" to others. This causes all manner of delays, and accidents. Unfortunately, the rest of us are counting on you FOLLOWING THE RULES/LAWS and therefore your actions create undue/unforeseen/unwarranted traffic congestion and altered traffic patterns. Examples are not going when it's your turn at a stop-sign; stopping traffic flow to allow someone to turn in front of you; not entering a round-a-bout when your quarter is clear; etc ...
IF ONLY PEOPLE WOULD FOLLOW THE RULES/LAWS, TRAFFIC WOULD FLOW SMOOTHER, BE SAFER, AND SELF-REGULATE.