Oh wow. So, my last job was at a software startup. Me and a coworker (who worked at the other end of the office, out of sight & hearing range of me) were constantly "harassing" each other. One day, I took all the wheels off his chair. He makes a point of limping by my desk, and tells me he hurt his leg falling out of the chair. 10 minutes later, my boss comes out and asks who hurt my coworker "because we don't have health insurance, also he's old and doesn't heal very quickly". I spent the afternoon feeling awful.

Fucker faked the whole thing & got our boss in on it.

This same guy also snapped out two of the pieces of my Rubik's cube and exchanged them with each other. I couldn't solve it for a month until I realized what had been done.

He had a habit of stealing my Rubik's cube and hiding it around the office. I come in to work one morning, and he's up on a stepladder in the kitchen, at one of the ceiling tiles. Weird, but I don't think to ask what he's doing. An hour later I notice my cube is gone. I start hunting around the office, and he says something along the lines of "You should try praying to your god above". I notice the ceiling tile that's propped up, clue in and get the stepladder. By this point, all my coworkers are watching me. I climb up to get my Rubik's cube back, and... nothing. He played me completely. It was in a potted plant near my desk or something.

I still work with the guy, but he's off on paternity leave right now. That kid's going to have an interesting life...

Another coworker is an amateur runner. A few years ago, he had a really bad day and ran a ridiculously high time on the track (for him)... let's say 10:15 (it's lower, but I don't want any googling to come here :-) ). His friend, another coworker, won't let him forget it. He just ordered the guy a book with the title "10:15". He texts him at 10:15 in the morning. And sometime? He'll wear a shirt with a clock showing "10:15". It's hilarious.