~When Orbiter is at the top of your start menu, and no matter how much time you spend on other programs, it stays there.
~When the pilot of your plane becomes unconscious and you volunteer to land the plane.
"Do you have a license?"
" *LAUGH* Sir, I play Orbiter. Who needs a license?? Nonsense I tell you!"
~When you re-wire your car with a joystick and throttle axis.
~When you pedal very hard on your bicycle trying to achieve escape velocity. That is, until a car cruises right by you casually, and kills your morale.
~When you develop the compulsive urge to strap a rocket to everything in sight to see how high it flies.