At the start of Grade 11, I photoshopped an image of one of our teachers. I gave him a blunt, sunglasses and a flip phone. I then proceeded to stick them all over, even on my own locker, which probably wasn't the smartest decision.
As for pranks made by you or the others, I have to admit, the one you pulled on Spike, where he sent dozens of scrolls to Celestia, was rather amusing to me.