I haven't actually let the air out of a rental before, but I booked a Chevy Cobalt one time, drove it a block, had the tire pressure light come on, and drove it back to the lot. They didn't feel like airing the tires to the proper level, so they just gave me a Dodge Charger instead. I'm pretty sure letting some air out of one of the tires would do the trick just about every time.