Existing pop songs in our universe, not originals written for the show. Bonus if it's a gay song, or sung by gay characters/actors.
Mine is the performance of Manilow & Tomlin's 'The Last Duet', sung by Tobias 'Toby' Beecher & Vernon 'Vern' Schillinger (played by Lee Tergesen & J.K. Simmons, respectively) on OZ. Out-of-context, it's a well-done showtune version with amusing choreo and surprisingly-decent vocals; in context, it's hilarious and shocking, as these two characters have a violent, torturous history between them, and while OZ does have prominent gay content it isn't the kind of show for surreal Cabaret moments.