Thought this was a fun topic - what else you got?
Go to the office in your pajamas and slippers.
Fill an empty gallon container with milk from the coffee station. (free at my job)
Place a giant March Madness bracket on the cafeteria wall. (very fireable offense at my job)
Bring in a pillow, and put your head down for an hour at your desk.
Turn on your out-of-office to indicate you have left to shoot a porn flick.
Send e-mail to the rest of the company to tell them where you're going. For example: If anyone needs me, I'll be in the bathroom.
Bring in and play with a hand held video game, with the sound on.
Put on a headband, wristbands, sneakers and an iPod, and powerwalk the hallways.
Use the Heisman pose as your hallway greeting to those you know.
Stand at a hallway intersection and request to see everyones ID badge as they pass.
Wear a headlamp all day.
Buy pants way too big, and pull them up to your chest for the day.
Every time someone in a meeting makes a suggestion, ask, Are you f****** kidding me!?
Ask random people in the office what sex they are.
Standing at one end of the longest hall, see if you can roll a baseball to the other end, without hitting a wall on either side.