People that don't understand the concept of a zipper merge, and get mad at those that do.
There is a stop light about a quarter mile from my work on a local highway. The stop light is a merge point, because there is an exit from a major highway onto the local highway at the light, so three lanes have to quickly merge to two lanes. They force the two to merge at the stop light, that way the major highway traffic has a clear runway into the other lane another quarter mile down the road.
So naturally, everyone coming from my direction should split into the two lanes at the stop light when it's red, then zipper-merge when it turns green. This keeps the flow moving, and everyone gets to start rolling at the same time as they take turns merging while moving, and avoids the snake-style, stop-and-go delay that a single lane provides when each individual car has to wait on the one in front of it.
I will usually pick the right lane, along with everyone else that works in our little business park area, because it gets you through faster if the cars in the left lane know that you are supposed to merge. But every day, there is someone in the left lane that is mad at people in the right lane for 'skipping' the line, as if it's an issue of morality and waiting in the miserable stop-and-go line with everyone else is the right thing to do.
And look, I get the idea of sharing in collective misery! I'm a Notre Dame football fan! But we don't NEED to share in this collective misery! Instead of getting aggressive and boxing me out when it's supposed to be my turn, and forcing me into the traffic dividers, or forcing the car behind you to deal with letting me in... just merge normally! I promise I'm not trying to line jump. I'm trying to use the traffic flow in the logically intended way. You shouldn't be throwing your hands up in the rearview or gesturing aggressively at me because I know how this works.
(Do I sound too pretentious about traffic flow?)