Drivers that use the shoulder for a mile before the exit they need when traffic is slow-moving.
Doing UNDER the speed limit in the left lane because, at some point, a left turn may be made.
Not paying attention to that 6ft arrow painted in the road with the words, right turn only, then going straight, effectively causing everyone else to slam their brakes.
Running red lights, consistantly.
Not knowing the size of one's car. If you can't judge, don't DRIVE it! Get one you can handle.
Holding kids on laps. I want to shoot darts at those assholes.
I want these:
http://www.roadragecards.com/samples.htm