When after watching the movie fight club, you begin to question whether your best friend is a real person, or an alter ego your mind has sub-conscientiously created.
Joe: (walks in) hey man, wanna play some Madden?
Dan: (points gun at himself)
Joe: Uh.. Dan.. why are you holding a gun to your head?
Dan: Not my head Joe, OUR head.
Joe: Uh-oh, Fight club syndrome.