CBS

Season 3: Episode 16 - Sandcastles in the Sand

Sandcastles in the Sand: When an old flame from a Robin Sparkles love ballad video comes back into her life, Robin turns into the head over heels 16 year-old girl she was the first time around. While the gang tries to help Robin see what a loser the guy has become, Robin has a hard time letting go of her past crush. But when he breaks up with her again, it’s Barney who finally helps her to realize how awesome of a person she has become. And in a shocking moment between them, Barney and Robin sleep together.