Hallooooo!
I'm busy with work. But not busy enough to not prank my coworker while he was on a three day field trip. In the fall, he lost a bet and I got to decorate his room with Stanford stuff (he is a ucla alum). It didn't bug him too much, but the kids carrying on about it drove him bonkers. I wanted to do something similar. He is a big ole prank-happy frat boy type, so I thought it was my duty to do something funny while he was gone.
So I set up a scavenger hunt around his room, leading to a big sign in the closet saying "You've been treed!" (Stanford mascot is the tree). When they got back from their three hour bus ride, they went nuts racing around the room looking for clues. I hid one hundred little cut out paper tree mascots around the room, so the kids will still be finding them in June (and driving him up the wall).
He also made the tactical error of giving me his car keys to move his car out of the teacher lot while he was gone. So I covered the inside of his car in tree mascots as well. Before I returned the keys, I made him pinky swear to give me a ride home. So I got to laugh while he pulled all the trees off the windows. I even taped a tree mascot to the air freshener tree. All in all, a good day.