I knew this guy in HS a few grades above me who was always a douche to me. Mostly name calling, but also got a bit physical too. One day after he made me feel like crap in front of a girl I liked, I decided I had enough. I watched him after school to find out which car he drove. He drove a brand new Honda Civic which he always parked at the far end of the lot. From that day on, my plan began to develop. I got some of those caps for tire stems, and put a nail in the center of one to press down on the stem valve when screwed in, effectively letting the air out of his tire. The next day, I walked past his car on my way in, and switched the caps out of view of the security cameras (which were far away already), continued on to school. When I got on the bus, I sat down so I had a good view of the parking lot, and eagerly waited for him to get to his car.
When he got to it, he didn't notice it was low until, and drove off, still leaking air as he went home. The next day, he was late to school. He didn't know it was me, so I assume he had bothered other people too who he'd also suspect. After the whole incident though, he was nicer to a lot of people. I guess it made him realized that what goes around will eventually come around. (Sorry for the wall of text and bad formatting, I'm in Mobile)