I really like the ten million little cups full of water all over everything in the room: floor, desk, bed. It works especially well when the victim is known to be at the bars getting drunk, and even better if they are attempting to bring a lady (or an hombre, depending) home.
I have also used the packing peanuts in a dump when the door is opened, although a better thing is a nasty old down pillow from a thrift store. Cut it open and use the down, it sucks to clean up. For extra effect rig the dump to a fan.
For something that sucks entirely to clean up: Cheap red soda and flour. Sticks to everything
For soap dispensers, replace the soap with oil. Somebody at the bar I worked at actually pissed in the hand pump soap dispenser, and at the end of the night one of the bouncers found out while "washing" his hands.