This isn't an uncommon gripe, and it's probably not very fair either, but when someone is in the right hand lane at a red light (when there are 3-4 lanes) who doesn't need to turn right. I know a small percentage of the time that person needs to turn right into a business or restaurant shortly after the light or what have you, but mostly it's a line of people who need to take advantage of that right on red but have to sit through the red light. I try not to be that guy but of course I am from time to time and when I am I do feel a minor amount of guilt.
This one might be controversial, an example: When I'm turning left and a car is coming from the opposite way, I will yield assuming they will maintain speed, but if they don't use their blinker indicating they are turning right, I have to wait on them to slow down, turn right, and then get behind them. If I saw their blinker ahead of time, I can squirt through.
People who turn out in front of you when they see you are obviously at a rate of speed that you are going to have to brake medium to hard. That's just inconsiderate and rude.
Lastly, People who need to cut across traffic and turn left and will wait forever until there is an opportunity for the traffic running left to right to let them through as well as the traffic from right to left to let them through, instead of just turning right and doing the first legal U-turn and letting everyone else go.