One time, I was very bored. Now I hate my school with a burning passion, so just for kicks (and cuz they deserve it), my friends and I pull pranks on the administrators, teachers, etc
So one day, I brought a fake turd to school. During lunch, I went into the lunch line in the cafeteria. Our lunch ladies are quite stupid, and when they weren't looking i put the poo in the french fries and ran!
When the woman finally turned around, she was greeted with a surprise. She totally flipped out (not like a ninja, though)! I could hear her shouting from a mile away! The next thing I know, the staff was dumb enough to think it was real, and they shut down the whole cafeteria! There were even health inspectors dispatched to our school!
I got away with all this. However, I do not recommend anyone else to try it, unless they are the type that will be sure to get off due to cleverness, stalth, or speed. It is fun to do even if the staff is smart enough to know it's fake, but It's even more hilarious if they buy it!