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a simple, everyday question that (when used correctly) can turn any conversation sexual; similar to the phrase "that's what she said".

person 2 questions "who's the guy" to imply that person 1's original comment was about a sexual act that they have committed and now the asker is simply wondering who person 1 is doing it with; extremely humorous when person 2 is a straight male.
Demorris - "I felt it comin and here it is!!!!"

David - "Who's the guy?"
by yourstepmom February 28, 2011