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.
song lyrics are sung by Billy Boyd, acting as Pippin, in 'The Lord of the Rings: The Return of the King,' and the movie stills, are from 'The Hobbit: The Battle Of Five Armies.' My favorite part of the movie.