Nothing irritates me more than people who won't drive the speed limit. I'm not talking about those who drive too fast, I'm talking about the ones who drive too slow!
As an example: I drive down a six lane highway (four car lanes and two bus lanes) to and from work everyday, about 15 miles each way. The speed limit is 45 mph, and since gas is so high, over $3.50 / gallon, I use the cruise control to keep from burning too much gas by going too fast. And it really pisses me off when I come up behind cars going 40, 41, 42, etc. miles per hour.
But if I try to pass them, I have to worry about being rear-ended by drivers going 50 - 55 mph in the other lane.
People think that speeding is the cause of auto accidents, but it isn't. It's cars going different speeds.
The slow drivers make the ones who want to drive the posted limits to slam on brakes, risking a rear-end collision. And the speeders weave in and out of traffic trying to get ahead of the car in front of them.
Dammit, people, just drive the speed limit!