9. Barney And Shannon
Another breakup explored in season one - albeit one that happens years before the current events of the episode- Shannon was the first serious girlfriend that Barney had. Through his retelling, the origin of Barney Stinson as a suit wearing ladies man is revealed, traced back to Shannon dumping him for another man right before the couple were set to join the Peace Corps abroad.
When a VHS tape given to Lily by Shannon is played for the gang, they see a Barney that is the antithesis of everything he currently stands for. The climax of the flashback sees that version of Barney wandering the streets when a flyer for a suit sale is blown into his hands. Thus the transformation, through a sequence that pays loving homage to The Empire Strikes Back, is complete.
It's fitting that the show directly compares Barney Stinson to Darth Vader in this moment, for this is the series of events that takes Barney to "The Dark Side".
While the character provides much of the comic relief of the series, there is no denying that he is emotionally broken, and having his humiliation laid out like this evokes feelings of sympathy that aren't normally associated with Barney. Yes, he proclaims that his life is "Awesome" at the end of the episode. But is he really fooling anyone.