If you spot someone getting into their car, and are waiting patiently for them to move their car out of their space. Some people take a really long time.
I agree that in areas where parking spaces are limited, people should be kind and not take forever getting into their cars. I rarely go to places where parking is limited though. It seems like every time I go to the grocery store, a car follows me as I'm walking through the parking lot, stops behind my car (preventing other cars from going around), and waits impatiently (glares and all) for me to leave, while not really leaving me enough room to back out... All when there's 172 other open parking spaces. This drives me crazy because I usually have a full cart to unload, a toddler to strap in, and I sometimes don't intend to leave right away anyway, but feel like I have to because someone is glaring at me and holding up traffic waiting for my space. Sometimes I'm just dropping off bags before heading into another store in the plaza, or grabbing something I forgot out of the car, or need to look up directions for the next store I'm going to before leaving. Of course other drivers don't know that, but c'mon, if there's another open space 3 spots past mine, drive to it and leave me alone.
Other pet peeve is bikes and motorcycles on the road. Bikes don't need to be on a 55mph curvy road in the middle of the lane going 25mph.
Motorcycles are dangerous white lining and when they don't follow road rules. Recently, I was first at a stop light to make a left turn on a divided highway. Turn light was red, but traffic going straight and the opposite direction was green. A motorcycle came flying up on my right side in my lane, almost taking out my mirror, swerved in front of me, and crossed in front of oncoming traffic to make a left. Oncoming traffic had to slam on their brakes to keep from hitting him and the biker took the turn so sharply and at such a high speed that he almost overturned his bike.