I humiliated my roommate
One of my former roommates was always going out drinking and coming home drunk, being very disruptive and making it very hard to sleep. I had a very busy class schedule at the time and this was beginning to impact on my grades. Frequently, she'd become so drunk that she'd pass out and need me and the other girl in the house to take care of her.
When the other girl got put on an extended work experience placement in another city, it was just me for a while. The drunk girl would never have any memory of her behavior and just assumed that she was having a good time. One night, she came back in and kept drinking for a bit. I went downstairs to turn the volume down on the stereo (again!) and found her passed out on the couch.
I was sick of her at the stage so I thought that I'd teach her a lesson. I stripped her naked and threw all her clothes into her room and then locked her door. I then kept her keys with the intention of just throwing them away later.
Then I got some superglue and put it on her right hand and pushed that into her hair so that she was left with her right hand stuck to the top of her head. I then glued both her feet together by putting glue on the bottom of them. I just spilled the rest of the glue around the couch and table so she'd just think she had an accident while drunkenly playing with it.
Then I left her and spent the entire day out of the house.
Apparently she freaked out when she woke up. She had no idea what had happened and obviously couldn't move properly. She tried to get into her room (it was a big struggle to even try) but couldn't get in and so couldn't get her cell phone. She had to use the house phone to contact the property management, who had to send someone over. She wasn't able to get dressed first so they saw her completely naked and exposed. They were able to open her room for her but they had to take her to the emergency room to deal with the glue. They got some clothes for her, but they weren't able to dress her properly as her arms and legs were otherwise occupied. They managed to cover her but it was completely obvious that she was glued together and that she was probably naked under there.
She was completely humiliated and personally, I thought that it was brilliant. Especially as she just blames herself and hasn't gone out to drink since. The best part is how far the story spread though.