My biggest pet peeve is people not using turn signals. Nothing I hate more than waiting on someone only to have them turn instead.
That's one thing I real like about some European cars. A lot of them have their turn signal stalk set-up so that you can just tap it and it will blink on it's own a few times. I never thought this was a big deal until I no longer had that option. Maybe some other companies have now followed suite? Crap like this should be standard on all cars.
Another peeve of mine about cars is when they don't have auto-down. My Mazda only has auto-down on the drivers side. I'd like auto up and down on both sides.