There really were no pranks at my HS. Man, I was deprived.
On the last day of school for seniors at my high school, a guy ran through the library in a Superman costume with a paper bag over his head, and then jumped onto the circulation desk from a ramp above it (our library was one of those multi-level things with stairs and ramps everywhere). He broke his leg in the process, so he couldn't get away before the librarian pulled the bag off his head.
No one ever could quite figure out what his point was.