Describes a situation where a heterosexual person can't truly determine the sexual orientation of a member of the same sex without engaging in an act that would question their own sexuality.
Also applies to any situation where a person who is, in fact, a heterosexual cannot proceed to do something that they want without strongly suggesting otherwise.
Guy 1: So what's the deal with Tom? Is he gay or what?
Guy 2: I don't know...Its hard to tell.
Guy 1: I guess one of us could go over there and try to make-out with him, but its a catch 69.
Guy 1: Hey, straight guys can wear skinny jeans, right?
Guy 2: Well sure straight guys can wear skinny jeans...its just that those guys tend to engage in sex with other men...