I keep locking myself out of my car. I did it 2 times last semester, and then I did it again this summer.
This time, since it's warm out, I left my windows slightly ajar. Well, I discovered a way to break into my car: I took off one of my windshield wipers and pressed the unlock button on the inside of the passenger door to unlock my car.
Important lesson: if you leave your windows cracked, make sure it's not too much that someone could stick a windshield wiper through. Though I guess someone could always stick a coat hanger wire in through a narrowly opened window.
(I guess the more important lesson is don't lock yourself out of cars, but that one seems more obvious)