One evening at work, I convinced my designers to help me build us a bamboo fortress without the rest of the team knowing, after they'd gone home. (The fortress is in theme with the project we are working on).
Sweetening the game, the entranceway to our new fortress environment is directly opposite the Environment Artist's area. Dude, you guys are the ENVIRONMENT ARTISTS - we're on your turf! Are you just going to sit there and take this?!? :-D
(I like to start arms-races)