Slap Bet

"Slap Bet" is the ninth episode in season 2 of the popular sitcom How I Met Your Mother. The episode, originally titled "Robin Sparkles", first aired on November 20, 2006. The episode received highly positive reviews and features in several lists of the best How I Met Your Mother episodes in the series. The episode led to two recurring jokes and storylines in the show: "Robin Sparkles", Robin's teenage pop star career, and the Slap Bet, in which Marshall slapped Barney at various points throughout the series.