Serge Gainsbourg and Brigette Bardot, 'Bonnie & Clyde' (Season 6, Episode 4)
As Mad Men slouched toward the Bethlehem of the late Sixties, its characters found themselves butting up against the fringes of the counterculture. Case in point: Joan and her friend, Kate, end up at the Electric Circus, the St. Marks Place nightclub that was a favorite of Andy Warhol, the Velvet Underground, the Grateful Dead, and a variety of other turned-on, tuned-out longhairs. True to the spirit of the place, Joan lets her guard down and makes out with a stranger, with the sultry French singers cooing at each other in the background. Tres chic, man.