1. People who don't signal. As a driver, you have only two truly useful ways of communicating with other drivers: your horn and your turn signal. And yet, most people around here seem more willing to use their middle finger than their turn signal. It infuriates me. Case in point: There is a corner on my way to work where I need to turn left at an intersection, so I put my signal on and wait in the intersection for a gap in the oncoming traffic. Nearly every single day, someone will be coming towards me at a clip that would not allow me to turn in front of them, only to zip into the left-turn lane at the last minute without slowing or signaling. At this point, of course, the gap will be gone and someone else will be coming at me. It drives me batty!
2. Overcompensators. I hate it when I am driving along the highway, at a safe five miles or so over the speed limit, being passed by a good 50% of the other cars on the highway, when all of a sudden, traffic slows completely to five or ten miles below the speed limit. Inevitably, I look out my passenger side window shortly thereafter to see the flashing lights of a police car with someone pulled over. I just don't get it. Slow down, fine, but you don't have to drop below the speed limit. Cops do not take an average of your speeds over the past ten miles when they pull you over. In fact, you're wasting your effort by slowing down now, because in case you didn't notice, SHE'S ALREADY GOT SOMEONE PULLED OVER! If she was going to pull you over, it would have been five miles back, where you were still speeding and she was hiding with a radar gun behind that billboard.
3. Unrealistic speed limits. There is a beautifully resurfaced road near me with a speed limit of 25. I try, I really do. But it's so easy to go too fast on that road. There is also a highway near me that is, if I should believe the signs and cones rather than total absence of work being done, currently under construction. At one point, the speed limit drops from 65 to 55 to 45 all in the span of less than a mile. And it is neither practicable nor safe for me to follow that speed limit when the people behind me are still zipping by at 75.
4. People who run red lights when someone else is obviously sitting in the intersection waiting to turn left. Seriously, I don't care how much you normally press your luck with a yellow light, if there is someone sitting in the intersection already, they should have priority because when the light changes, they could DIE.
5. Gas prices. 'Nuff said.