Marshall was given a choice: 10 slaps immediately, or 5 slaps to be delivered at any time in the future. Barney, in his infinite overconfidence, chose the 5 slaps, unknowingly signing up for years of psychological warfare. A History of Violence: The Slap Timeline

The Slap Bet was born in Season 2, Episode 9, titled "Slap Bet". The stakes were simple: Marshall bet that Robin was hiding a secret about being a porn star, while Barney bet she was hiding a secret marriage. The prize? One slap, as hard as possible, to the face of the loser.

You can't have a civilized slap bet without oversight. As Commissioner, Lily’s job was to: Rule on who actually won the wager.

Throughout the series, Marshall used his slaps to punctuate major life events and holiday traditions: HIMYM: 8 simple rules - What's Alan Watching?

Whether you’re looking to settle a dispute with a "Slap Bet" of your own or just reminiscing about the best episodes of HIMYM , here is everything you need to know about the rules, the history, and the art of the slap. The Origin: Robin Sparkles and the First Wager

When it was revealed that Robin’s secret was actually her past as Canadian teen pop sensation , both men were technically wrong. However, Barney prematurely slapped Marshall, leading to the appointment of the world’s first Slap Bet Commissioner : Lily Aldrin. The Role of the Slap Bet Commissioner