I did a couple of things.
1) i was babysitting my cousin one day and he was suppose to be doing his homework but he was taking a nap instead. I took a bowl of warm water and poured it on his crotch. He woke up thinking he peed on himself and i let him believe that for like 2 weeks.
2) i pranked my wife by making her think i was sleeping in the bed with another woman. I took a long sleeve shirt and a pair of jeans and stuffed them with dirty clothes. Then i took a basketball and an old black wig from a halloween costume and covered it to look like a head. I layed the stuffed shirt, stuffed jeans, basketball and wig under the covers in our bed and laid next to it like i was cuddling with it. My wife went hysterical. I was smiling and kept telling her "Its not what you think." She was screaming, crying and all other types of shit until she finally yanked the covers off. She was still kinda mad but she couldnt help but lol because she knew i got her good. Best prank ever.
3) one day my friends and i were getting drunk and we decided to prank one of the guys who was super drunk. We put did the old see through wrap under the toilet lid trick and made him smear shit all over himself when he went to the bathroom. He was too drunk too realize what happend and thought he just didnt wipe his ass good enough. We were so terrible but it was so hilarious.