xkcd

Nothing like getting to a 4-way stop and the cycle is going smoothly then some dipshit starts waving cars and throws everything out of whack and next thing you know everyone is inching forward at the same time.

Equally bad, the entry drives into shopping centers are often made to not stop when entering the lot, this way during busy shopping times traffic won't back up out into the street. This is a normal, common thing, usually plastered with signs "INCOMING TRAFFIC DOES NOT STOP" and you still get people stopping and waving cars through, thinking they're doing anyone a favor, when instead it's confusing everyone as to what the rules are at the intersection. Then cars start driving around each other and you get to hear that sickening "scrrrunch-POP" as the other lane started moving without noticing the rules had changed.

I have a feeling these are the same people who push a full cart into the self-checkout having never used a self-checkout in their lives.