Oooooh, I forgot the best one, from Queen Anne High School in Seattle.
My buddy Charlie discovered that you could do something with a transistor and a tiny speaker that made a sound like water drip-drip-dripping into a cistern. So he did so, attached it to a solar cell in a nearby basement window, and installed it in the main top-to-bottom air shaft of the school. If you sat in the room next to the shaft, you could hear the irritating drip-drip-drip all period long. Many complaints were lodged, but the janitors could never find the source of the sound.
Years later he met someone at a party who was introduced as having gone to the same high school as he. He asked her if she ever was in room whatever, and she said yes, and he asked if she remembered the drip-drip-drip sound. She said yes. He explained it was his doing. She slapped him.
Later they got married.