What started from taping something on someones door or cube wall escalated into the following.
This past year we had an intern turned hire. His desk is only partitioned on 3 sides as most cubes are and 2 of them were half height as they are part of a walkway. Anyway, he was traveling for a week and we basicallly constructed a dummy of him from boxes and photoshop. Put it in his chair and built a house out of cardboard around it complete with a working door, windows, roof and satellite.
Another guy got an office filled with balloons 3-4 feet high and put all around his desk and path to the desk. Kept them in place with packing cellophane and took every large potted plant from all the offices and elsewhere and put them up against the wall of balloons. Hit the lights and close the door.
Can't do anything too bad in my place. One guy though sent an email as if it was from said intern/hire to the president and some others asking for the day off early to go catch Brokeback Mountain with a special friend. Intern was not pleased.
Oh yeah, and another person told me of one time they called a hotel they knew someone was travelling to before they actually got there. They posed as the person and asked for rubber sheets put under the mattress because he had a bedwetting problem.