Chubby Checker, 'The Twist' (Season 1, Episode 8)
It can be hard to remember now, but when the series began, Peggy Olson (Elisabeth Moss) was just another girl in the typing pool, and Pete Campbell (Vincent Kartheiser) was simply another smarmy salesman. Even though their relationship eventually settled into one of begrudging respect, it began a brief fling before the whole thing imploded (and resulted in an unfortunate pregnancy). One of the most memorable moments from their tryst happens in this episode: The whole office is drinking at P.J. Clarke's when someone puts Chubby Checker's dance-inspiring hit on the jukebox. Hips are twisting; inhibitions are loosening. And then Peggy slinks her way over to surly Pete — who drunkenly spurns her.