A "Cap Trick" is when Mike Green of the professional ice hockey team the Washington Capitals tricks people into thinking he is worth the space he currently occupies, when he, in fact, does not.
Guy #1: "Whoa man, check it out! There's Mike Green, totally deserving of the space he's currently occupying!"
Guy #2: "No man, he actually doesn't deserve any of the space he occupies, ever.
Guy #3: "Oh snap. That's a Cap Trick if I've ever saw one.
Girl #1: "I'm never having sex with any of you."