h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How about some Doom style entries, like...
You know you've been playing Doom too much when:
...You don't understand why thrown objects don't automatically compensate for elevation.
...Whenever you see a fat person you start looking for their Rocket Launchers.
...The words 'Find Some Meat' flash across your mind whenever you see a chainsaw...
...You don't squash spiders, you shoot them.
...You see a box of tomatoes and expect them to start spitting Ball Lightening at you.
...You shoot all your friends because you think your in a Deathmatch.
...You walk into walls, expecting them to open.
...You break every bone in your hand trying to open the door by punching.
...You think the local Disco is actually the 'Club Doom' level, accuse everyone inside of being Ravenants, and blow the place to hell.
...You consider a Chaingun to be a sidearm.