In college, my entire dorm floor went to someone's house for the weekend. Me, my roommate, and a few others were behind b/c of work and such. On our dorm floor there was one larger room called the "quad" which has 3-4 people instead of 2, and there's also a kitchen room in the middle. We gathered some other random people to help and switched everything from their dorm room with the kitchen (furniture, beds, appliances....EVERYTHING got swapped). These girls had a LOT of stuff! It took a few hours but it was great. We joined the party like nothing happened. When we got back and they saw it, they were totally convinced a group of their guy friends had done it! They even lived in the kitchen for a few days b/c there was so much stuff to move back.
The year before, I remember Phil called me one morning and said he woke up to a chicken in his room and he had to clean up chicken poop. He was the RA so he didn't share a room. I guess the chicken was some sort of prank on the RA, but he just shoo'd it out into the hall and went back to bed. Somehow it got outside, then all the animal rights people freaked out and someone took it to a farm or something.
In highschool, my prank was an epic phail b/c someone stole our idea and totally ruined it. A friend and I thought it would be a great senior prank to buy a bunch of pre-greased piglets and release them in school, running wild and squealing but not able to be caught. She said they were $40 a piglet and came pre-greased, so we would get as many groups of 4 as possible and each person would contribute $10. Some idiot caught wind of the prank and instead, bought an adult pig from a farm auction and pushed it into the school through a back door. The pig just peed all over the floor and sat there. Again the animal rights people freaked out and someone took the pig away.