No one here is feeling particularly pranksterish currently.
However, I wrote a haiku back when we had a project close out that I quite liked:
errors have been made
the project has been shut down
others will be blamed
Actually, I had a whole "corporate haiku" line that all ended with the "others will be blamed" phrase.
In the past: we had a prankster co-worker who was on vacation. While she was gone, we took all the personal photos off her cube walls, and replaced her file cabinets with some from an empty cube. We borrowed some family photos from someone she didn't know, and put them up in the cube. We changed the name on the outside of her cube and put a big "Welcome to our Group!" balloon in the cube. It was great!
We have had cube decorating contests which were quite entertaining.