Definately- people shortcutting through your campsite.
Other pet peeves...
1) People who lock their car doors with their remotes and their vehicle confirms with a flashing lights and a loud chirp of the horn. Love it in the middle of the night
2) Load music after midnight
3) Dogs from neighboring campsites that tend to roam around your picnic table and relieve themselves in your campsite (yes, it did happen to us).
4) I know it's gross, when you camp in a location with modern plumbed restrooms and then you find that some people still won't flush the stuff down!
5) Rude campground management / staff.