One of few euphemism for cunt despite being one syllable longer and possibly more offensive as it implies that women will only sexually obey men who give them money.
Mark: "Say, why aren't you with Jennifer?"
Steve: "Girl broke up with me 'cuz I called her a coinslot last night."
Mark: Dude, you're unemployed. You can't afford a fine 75 cent coinslot like her!