People who don't accelerate up to highway speed before pulling out in front of you. Then after you hit the brakes, they immediately put their signal on, jump into the left land and gun it.
Commuting has been boiling my piss lately. Some guy in a dually Cummins RAM pulled up in the left lane next to me at the last stoplight before the highway. 6" sewer pipe exhaust and tuned to roll coal. He was decent enough at the get go, and he slowly pulled away from me. As were travelling down the highway, bumper to bumper traffic, I see a hero in a white BMW jumping in and out of traffic behind us, pulling in and out of gaps barely bigger than a car. After running out of gaps, he decides to pull out into the dedicated mass transit lane on our right and blast by everyone for about a quarter mile or so before yanking his car back into traffic and into the fast lane, right in front of mr. coal roller. Well, you can imagine it didn't go down so well. Cummins guy decides to pull over onto a wide left shoulder and toenail it, belching out a huge bank of sooty exhaust until he was in front of BMW guy. The he proceeds to roll on and off the throttle for about a mile, dumping his sooty waste all over the front of the BMW. I had a hard time deciding who was the bigger douche.