The title of the episode is a take-off of Love, American Style.
On Valentine's Day, Homer and Marge get stuck in a Tunnel of Love ride after Bart turns the water into Jell-O. To pass the time, the family tells stories of famous couples: Bonnie and Clyde (Homer and Marge cut a path of crime through 1930s Springfield by robbing banks), Lady and the Tramp (Homer and Marge again; this time, as the eponymous dogs from the classic Disney movie), and Sid Vicious and Nancy Spungen (Nelson and Lisa are punk rockers in love and addicted to chocolate).