glue some pages of their daily planner together....not the entire page but a spot right in the middle so that when they open their book and open the page quickly..rrrip...".oops was someone messy with something last time that they were in their planner?"

A dead fly/bug or a hair is also lovely to find in one's brown paper bag lunch/sandwich/food.

Or simply stare through the tines of your fork and pretend that they are in Prison for the Criminally Stooooopid.

~~I am having waaaaaay too much fun with this~~