Had this friend in 8th grade who was kinda normal, me and a buddy decided that we wanted to have some fun so we alienated him for a week and then became friends with him for a few days, and repeated this. We gave him really really bad advice for talking to girls and he constantly embarrassed himself but we told him it was normal.
He said one day that he had a girlfriend (who was the ugliest girl in our grade) and then we went and asked her if she was dating him and she had no idea who he was.
He also had this blood disorder that caused him to bruise really easily, so we made him get into conflicts with people and one day someone threw a strawberry at him and his entire tit bruised (he was really overweight).
On top of that he had a phobia of bugs and we often put insects and crap on him and he would freak out and start yelling. We put a rhinoceros beetle on his shoulder one day and it started hissing at him and cause he was fat he couldn't reach it so he looked like he went full on retard, flailing about and ****, which was probably one of the funniest things I've ever seen.
I put a biscuit on his back when he was bending over one day and told him an insect landed on him and he started screaming and saying he could feel it crawling down his back.
In final year we had told him he could dance really well even though he was absolutely terrible so he went to the end of year talent show and made a fool out of himself in front of 800 people.
There was another kid who probably had autism, so I bought him a harmonica and he played it all the time, but it wasn't really playing it was just really loud obnoxious noises and it really pissed the teachers off.
In 12th grade me and a friend decided to make some blue toffee and make it really thin and we sold it to some kids and told them it was crack, and they bought it and then we tried selling it to a teacher and we got talked to. We also put it in a kettle and pretended to get high off it and ruined the kettle in the process.
Also one of my 'forever alone' friends said he had trouble getting a girlfriend so we said if you give us your number we can get some girls to message you. So we printed out a "lost" flyer with a picture of a pepe dog and put it up all around the school with the kid's phone number on it.
I went to boarding school so I did a lot of ****ing stupid ****. The above is the fun we had with day school students, when I was in 9th grade we had a dorm parent that was really creepy so we implied that he touched some of us without directly saying it and then he quit the job about 2 years later.
About the time that jackass was a big thing we decided to do a video series of in-dorm-jackass which included branding a kid with a fork (we heated it up in the kettle), whipping eachother with tea towels and someone ended up with their ass bleeding, drinking raw eggs and turns out someone was allergic to raw egg, 3L milk challenge, and the list goes on.
We also played black hawk ninja, which was this game that we played with one of the dorm parents who had poor eye sight. At night time when we were meant to be in bed, we would dress all in black and run around the dorm and hide in plain sight. We would make a noise to get his attention and have to run around to as many quadrants with the quickest time without being caught. We made the poor bastard's life real hard as a dorm parent.
We also had a dorm parent who made music and was at university and we told him his music was terrible and then spread rumors that he was gay. He cried one day and left a week later. He was only there for 2 months.
Now that I think about it I was a real **** of a kid in school.
EDIT: Oh yeah, the kid in 8th grade is completely socially awkward now. Poor guy.