Duct tape lunch meat like bologna to the BACK of drawers - dresser drawers work best - WEEKS later, there is an unidentifiable stench from their room that will take another few weeks to source!
Also knew someone who "castrated" all the mice at their office - took all the balls from every computer mouse - with laser ones, doesn't work as well, so now we put a piece of electrical tape over the sensor!
ANYTHING with jello is funny!
Used to call my classmates and pretend I was with the dean's office - stated they hadn't paid tuition and needed to rectify asap.
Of course, being in vet school - someone MAY have taken three sheep, labelled them 1, 2 and 4 and set them loose in a student residence building... (not original, but you never wanted to take a chancem, so always end up looking for the non-existent #3!!!)