"You know how I know you're gay? You didn't win the Superbowl."
"You know how I know Rex Grossman is gay? His favorite band is Coldplay."
How do you know your movie producer is gay?
You know how I know you're gay? You have a pumpkin with Steve Carell's face.
How you know your couch really sucks.
Wine glasses - that's how you know it's a classy party.