I heard of a prank that took place several years previous to me attending college. There was a group known as “The Flooders”. They got this name, because they turned a shower room in a common bathroom into a pool by closing up the doorway, and plugging the central drain. It was an engineering school, so the strength of the walls, and doorway planks was calculated properly. The pool was a success. The problem involved the strength of the floor apparently. Hence the name.
They allegedly drained a man-made lake as well.
A crop circle would be a cool idea- Just set aside enough time. It’s faily tiring.
Since the last few posts in this thread have expanded the prank concept from High School to College, I figured I’d mention the all-time best prank I’ve ever heard. Many, many moons before I attended the liberal-arts college I currently have the pleasure of attending, a group of students recieved word that Dan Quayle would be visiting town. (This was during his tenure as Vice President, and actually I believe it was during the Gulf War) They cooked up several dozen pounds of mashed potatoes and mixed up three batches. One portion they colored with red food coloring, one with blue, and one they left colorless. They hightailed it downtown, taking up residence outside the building where Danny Boy was speaking that night. When the appointed hour came, they all discretely swallowed ipecac, and simultaneously vomited red, white, and blue-green (some minor food color issues, I guess) mashed potatoes on the downtown streets, flipping out most of the other prostesters/media/passerby. They called themselves the “reverse peristalisis painters”, and still hold a cherished place in the collective memory. Gawd bless 'em.