In the world of How I Met Your Mother, running gags are not just common, they're an essential element of the show's humor. So much so, jumping coldly into the show during its fifth season guarantees a minimum of three jokes per episode going unnoticed, or at least underutilized. These jokes include catchphrases (Legen " Wait for it " Dary), character traits ("salute; Colonel Stuck in my teeth"), and even subtly revisited jokes ("Salmon. I'm going to say that again: Salmon.")
Quite possibly the grandest among all the running jokes is The Slap Bet. First appearing in season two, the slap bet has arced in and out of various episodes, including this week's, where it took center stage. For those not in the know, the slap bet was a wager between Marshall and Barney about Robin's closeted past. In lieu of money, the winner got to slap the loser. After believing he won, Barney prematurely slapped Marshall. Upon discovering he had indeed not won, Marshall was granted permission to slap Barney five times whenever he pleases for revenge. Being nearly twice the size of Barney, Marshall relished the decision. The first slap occurred immediately, the Minnesotan leviathan hit the scrawny womanizer so hard, he immediately hit the floor. The next occurred several months later in retaliation for repeatedly insulting Marshall's wife, Lily.
Read our full How I Met Your Mother Recap here.