Planting a garden in a keyboard. Best office prank idea, especially if the co-worker goes on vacation for a week or so. I would use a keyboard that looks like theirs though. That way you don't get into trouble for destroying someone's property.
Chauvet Intimidator Trio LED Moving Head Intelligent Lighting
Chauvet Intimidator Trio Warehouse Resealed is an innovative, LED-powered moving head with beam, wash and effect features. It allows you to seamlessly change from a narrow beam to a wide wash with the motorized zoom.