You attempt to change lanes on the freeway by strafing left.
You keep trying to pick things up by walking over them.
You eat the blue and green balls off the Christmas tree.
You feel lousy and look down for the status bar.
You grab your kid's backpack and can't believe it's empty!?
Your desk at work is piled with paper because you refuse get too close to the recycle barrel.
The only way your spouse can get your attention is to throw tomatoes at you.
Your PC boots straight into DOOM unless you press a key.
Your desk is wearing away right in front of the arrow keys.
You back-up your DOOM files daily.
You try to double click on every door in the house.
You use the alarm clock to tell you when to GO to bed.
Your seat cushion doesn't return to normal upright position.
You dress up as your favourite DOOM character for Halloween (and your friends still know who you are).
You will try to turn to get out of chair by moving the trackball in that direction before you stand up.
You expect every door to open up, not in. (this can be quite painful sometimes)
You throw open the door to your house, jump backwards, and shoot your mailman.
When on your way to work you scan the streets for medkits and ammo.
Going into a room or getting off an elevator, you run in and out quickly to see what follows you out.
You don't worry so much about getting hurt, since you'll probably pick up one of those blue spheres somewhere.
Watching someone come out of an elevator makes your mouse finger twitch.
You start side-stepping into rooms.
You push on walls as you walk down the hall, looking for secret entrances.
You reach for your chainsaw when your wife's cold gives her the sniffles.
You instinctively target trash cans while walking around campus/work.
You look for sniper spots above you when getting in an elevator.
You can't stop squinting as you walk around your house.
You think you can actually walk through walls.
The border and status area are burned into your monitor.
You know ALL the ID codes by heart.