I personally have done some terrible, Terrbile things to rental cars...... some of them include
Removing the air filter (and not putting it back)
I drove a new Volvo from Maine to NYC while my passenger at any time would pull the shifter to LOW 1
Puked in above mentioned Volvo
Took a jump over railroad tracks in a Pontiac Supercharged Grand Prix and blew a tire
Drove a Nissan Sentra up on a pile of bricks(only the drivers side though)
Took a Saab 9000 Turbo to Epping for the night (best run 15.0!!)
poured oil on the ground in 2 places (where the front tires go) and proceeded to set the ebrake and go to town (on above mentioned Saab) <- pretty sure the marks are still in the road in south portland leading to the Fed Ex airport hangar
Flew a kite out the back of a rented Mustang Convertable
did so many neutral drops in a rental Neon that the car was stuck in drive (forever)
This was back when i had little respect for the law..I've grown up a lot since then