My Pet Peeves:
Driving-
Parking over the line in a lot. This bugs the hell out of me because it causes something I call "Cascading Parking Failure". They effectively take up two proper spaces, but there will always be someone willing to park incorrectly in the space next to them so that they, too, are over the line. This error can propagate over several spaces if no one corrects by parking closer than usual to them. The worst part is even if the original culprit leaves, there's still cars parked incorrectly and the problem is perpetuated long after the first idiot is gone. Seriously folks, it takes at most 15 seconds to pull your car back and adjust in a parking spot.
Turning on your turn signal when merging after you're halfway into my lane. Please, don't even bother.
Freeway follies. These include: People that speed up when I try to pass them. People that speed up to pass someone, then match speeds when they're right alongside the car they're passing. Zoning out on cruise control set to the speed limit in the fast lane and not noticing the caravan collecting behind you. Accelerating to cut me off when I put on my turn signal after matching your speed.
That last one has inspired a rant: Seriously folks. Relative speed matters more than position on the freeway. Just because I'm in front of you doesn't mean I'm going to "win". Also, any microsecond you've gained on your trip by maneuvering to get in front of me so you can be first will be lost at the next stoplight. If everyone were sensitive to the speeds of people around them, the average blood pressure on the road would go down.