I was 16, first ever oil change I'd done by myself, '76 Pinto 2.3L I4. I drained the oil, changed the filter, and proceeded to refill. I put four or five quarts in and checked it. Nothing on the stick. Put in three more, checking the stick each time, still nothing. Went to get another quart and my foot slipped on the concrete floor. I was standing in a puddle of fresh oil, I'd never put the drain plug in. It hasn't happened to me again since.