You really need to work with your resources and know your audience, but here are a few ideas to get the creative juices flowing:
- Filling/covering a person's office/cubicle with [fill in the blank with your favorite material]
- Rendering a person's computer or phone useless through the use of clear tape (e.g. taping bottom of mouse or hang-up button on phone)
- Replacing person's computer and monitor with similar-shaped objects (e.g. microwave and toaster)
- Sending "private" e-mails from a person's unlocked computer
- And of course the old classic "acid in the water cooler" trick ;)