Ah... campus pranks. You gotta love them.
Here is a small list of pranks I played on other people during my years as a university student:
[1] I was working at a pub to make some extra money and there were these really annoying people sitting at the bar. I think they were psychology students. Anyway, they were really noisy and drunk and violent and they were doing their utmost best to piss me off, throwing beer at me, throwing their cigarette buds in the sink one uses to rinse out the dirty glasses, stuff like that. So, I took a small break, drove my bycicle to my 'kot' (the room where I stayed as a student), took that bottle of laxative (which I had bought for a similar occassion, by the way), drove back and gave them each a cocktail on the house. It took another 40-50 minutes before the laxative actually started working but seeing them flee to the toilet non-stop, their hands against their buttocks out of fear that the shit might otherwise ooze out, well, that just completely made my day.
[2] As I said, I bought the laxative for a similar occassion: in my 'kot' I had to share a kitchen with five other students and one of them kept stealing my Dr Pepper. I didn't know whom it was, so I bought a new bottle of Dr Pepper and poured half a bottle of that laxative into it. Two days later the bottle was gone and three days later I heard someone in the kitchen talk about how 'Peter had had really bad cramps last night and how it probably was from eating a bad kebab.' A couple of days later I ran into Peter on the stairs and told him 'to keep your fucking hands off my Dr Pepper, you piece of first grading shit!' Never happened again.
[3] The first and second year at university, I stayed in a dorm. And dorms are fun! They also have communal kitchens with communal fridges and communal showers and communal toilets! Communal stuff is great because if you wreck it, a lot op people get pissed but they don't really know whom to blame because it is communal stuff! Duh!
One thing me and two friends often did, was clog up all the toilets from a certain floor with lots and lots of toiletpaper and then flush those toilets multiple times until they leak water all over the floor. It was a risky thing to do because there's always someone who needs to take a shit or a piss, but life in the dorm kinda sorta stopped at 3 or 4 o'clock in the morning, so that was the perfect time to do it. The toilets were really close to the stairs and one time we actually managed to get them to leak water from the sixth to the fourth floor. Brilliant but not very nice, I agree.
[4] Ever made sperm pancakes for some girls you invite over? I did this with three guys from my last 'kot', my last year as a student. There were just the four of us in that 'kot' so sometimes we invited some girls over to drink and smoke pot and fuck and shit, but one day we had this brilliant plan of making weed-pancakes for them. So we were preparing the dough and we were already fucking stoned, so one of us started about 'wouldn't it be fucking gross if we all jerked off in this bowl and made sperm-pancakes for them ladies? So we did. We made 100% not to eat one of those ourselves and actually served them to some girls from third year Economy (I think it was). There was weed in them as well, so it can't have been that bad.
[5] A guy from that 'kot' also had a recurring urge to shit in this other guy's jar of chocolate spread. He never actually put the shit spread on bread or in his mouth, though. The scent was too dominant once he opened the lid. That happened like twenty times that year. It was like a weekly thing, the shit in the jar of chocolate spread. Totally gross.
[6] It was forbidden, but during the warmest months (May, June) when everyone was studying really hard, we often threw water and water balloons out of the dorm (1st and 2nd year). One day, me and the same two friends who liked clogging up the toilets, went up on the roof of the dorm (which they later closed, I heard, because it was becoming way too popular as a suicide location), and started filling balloons with pee (we only got four or five of them) which we dropped on a young couple who were making out in the grass in front of the building. The guy was furious and ran into the building, probably with the intent of kicking our arses. We were back in our rooms in like 5 seconds and never saw him. Fortunately.
There's lots more, but I think these are the funniest ones.