Log on, wait a sec, then get a frightened look on your face and scream, "Oh my God! They've found me!" and bolt.
Laugh uncontrollably for about 3 minutes and then suddenly stop and look suspiciously at everyone who looks at you.
When your computer is turned off, complain to the monitor on duty that you can't get the darned thing to work. After he/she's turned it on, wait 5 minutes, turn it off again, and repeat the process for a good half hour.
Type frantically, often stopping to look at the person next to you evilly.
Before anyone else is in the lab, connect each computer to a different screen than the one it's set up with.
Write a program that plays the "Pokemon" theme song and play it at the highest volume possible over and over again.
Work normally for a while. Suddenly look amazingly startled by something on the screen and crawl underneath the desk.
Ask the person next to you if they know how to tap into top-secret Pentagon files.
Use AIM to make passes at people you don't know.
Make a small ritual sacrifice to the computer before you turn it on.
Bring a chainsaw, but don't use it. If anyone asks why you have it, say, "Just in case..." mysteriously.
Type on VAX for awhile. Suddenly start cursing for 3 minutes about everything bad about your life. Then stop and continue typing.
Enter the lab, undress, and start staring at other people as if they're crazy while typing.