When I was in my second year of college, my girlfriend at the time was a high school senior (class of 1977). One day she drove to school, got out of her car, put her books on the roof, and started talking to a friend. When it was time to go in, she locked the car door, grabbed her books, and they walked in together. That afternoon, she couldn't find her car keys. They were still in the ignition and the engine was still purring away. She had to go inside (no cell phones back then), to call her parents to bring her spare key. 1/4 tank of gas wasted, but zero harm done to the car.
-Irish