Whenever answering the phone, and it's for your boss, say, "He's under his desk screwing his secretary. Can I take a message?"
Strip off all your clothes. Complain about how hot it is in the office, regardless of the temperature.
When your boss is on the phone scream, "Damn it! I'm expecting a call!! Stay off the phone!!"
If your boss bumps into you, start screaming sexual harassment. Talk in great lengths about the state laws on harassment. Get the authorities involved. Threaten to sue.
Sleep with your boss's daughter. Videotape it. Pass out copies around the office. Brag about how easy she was.
Steal various office equipment (pencils, staplers, desks). Frame your boss for it.
When asked to do something start laughing hysterically. Continue this for five minutes. Calm down and say, "Oh, you were being serious?"
Loosen the bolts on the boss's chair. Laugh loudly when he/she falls down. Play innocent.
Whenever the boss starts to tell you a story, interrupt him/her with a story of your own. Make sure the story is boring and has no point whatsoever.
Send a dozen roses to your boss's house when their spouse is home. Sign an ex-flames name on the card. Next day, ask him/her how their evening was. Be obvious.