Every time a reference is made to Mulder's obsession with porn. Every time Cancer man lights a cigarette. If they ever drive a car other than a Ford Taurus. Every time Deep Throat or Mr. X is called. Every time Mulder mentions his sister's abduction.
Every time Scully is seen examining internal organs of some corpse.
Whenever Mulder runs off and leaves Scully to get attacked just so he can save the day. If Mulder or Scully is in a dark scary place and one of them drops or loses a flashlight. Revised Standard X-Files Drinking Game 1. Every time Mulder and Scully talk on their cell-phones. Any time Mulder or Scully is seen eating or drinking anyting.