Season 3: Episode 9 - Slapsgiving

Slapsgiving: Over Thanksgiving, Robin and Ted experience a backslide that starts with a joke Ted makes about Robin's new, older guy, then leads to a fight, which leads to them sleeping together. The backslide forces them to question whether trying to remain friends after a breakup is too difficult. Meanwhile, Marshall has set the slap bet countdown clock to expire in the middle of Thanksgiving dinner, so throughout the day, he torments Barney about the slap that is inevitably coming.