Finger prints on the windows
Slamming the door
Slamming the boot lid
Taking shoes off and putting feet on the dash (actually happened, I really wanted a switch to deploy the airbag for that one)
Leaving trash or making a mess
Shoe scuffs on the door
Tracking excess mud or snow inside
Leaning equipment/gear against the paintwork
Placing items on the roof, bonnet or boot lid
Complaining about my music
Complaining about me making you wear a seatbelt
Calling me Obsessive Compulsive or "Anal" because my car is clean
And my all time favorite, when I was driving my 1976 Volvo 245 DL, I gave my uncle a ride back from returning a rental truck.
Uncle: This car is just like I remember it. It's loud, it's uncomfortable, it's got crappy accelleration, it's got crappy handeling-
Me: IT'S TAKING YOU HOME!
Again in the same car, while giving a girl a lift home - I was hoping for a date (note, my car was posessed, like a cross between Herbie and Christine):
Pulled up to a stoplight after 3 blocks of the girl ragging on my car. As we pull up the engine starts to misfire, nothing bad, but I can feel it. The whole time the girl is going on about how crappy my beautiful car is. Finally the car just dies, right there at the light. The girl, of course, seized on this and continued on. I cranked over the motor but it would not fire, finally I stop and turn to my passenger.
"You need to appologize, you don't bad mouth a man's car"
"You're right, I'm sorry"
"Why are you talking to me?" *points at the dash*
"Oh you have to be kidding"
"She's sensitive and won't start unless you appologize" *cranks engine again*
"Ok, fine, I'm sorry."
"Like you mean it." *cranks engine*
"I'm sorry, you're a good car, a classy car, a collecters car in the making"
"Now give her a pat on the dash, right there over the clock, she likes that"
At this point I start to crank the engine, the girl pats the dash, the motor fires, light goes green and we pull away with no more missfires. I never did go out with her, but just as well.