I think the inability to maintain consistent speed is my biggest pet peeve on the road. I hate when I move over to pass someone, get to their door and they speed up and match me, or when someone passes me, then falls back, passes me again, shoots a mile ahead, falls back again
I also cant stand people that fly through parking lots. Seriously, why do you need to do 30+mph in a damn parking lot where people and kids are walking?!