People that are turning left and pull up past the line so they are blocking your line of sight when trying to turn right.
You're supposed to move out into the intersection when waiting to make a left turn.
It's people who wait behind the line that irritate me. 
I always wait behind the line if I'm the second vehicle as I can't trust the person in front of me to actually make the left in time for me to proceed after. It seems more and more people won't make the turn until the light is red even if there's nothing coming. Also, the fact that even if he/she is competent, they can't get through because of the two or three cars that run the red coming the other way.
When I learned to drive, I was taught that at least two cars should be able to turn left on any light cycle. Only way that is going to happen is if the first car moves fully out into the intersection and the one behind at least noses out in front of the line.
If you're already in the intersection and the light turns yellow, then you can legally make your left turn. But if you're stopped behind the line when the light turns yellow, then you can't legally enter the intersection, so you're stuck there.
But I agree. I learned to drive 30 years ago when it wasn't common to have three cars blowing straight through on a red. Unfortunately, I guess one car turning left per yellow is the new norm. Nowadays, if I'm the second car I'll wait behind the line as well. Not that there's usually the option, as the first car rarely pulls out enough anyway.
