Lily and Marshall attempt to raise money to repair their floor by selling off Lily's designer clothing. Lily also discovers an alternative use for her art. We find out it was Abby (Britney Spears) that was Barney's relationship saboteur.
When Ted breaks Stella's trust by telling the gang she hasn't had sex in five years, their relationship becomes rocky. Meanwhile, Barney is desperately seeking a new bro and tries to make one out of a co-worker (Will Forte).
Robin's old boyfriend, Simon (James Van Der Beek), from one of her old pop videos comes to town and they attempt to rekindle their old romance. Barney quests desperately to find the video of her second song which also features Alan Thick and Tiffany.
When Barney's love life is being sabotaged by a mystery woman, he sets up a tournament bracket (a la the Final Four) to determine out of 64 women which hates him the most and is most likely sabotaging.
Ted is still seeing his dermatologist Stella (Sarah Chalke) to have his butterfly tattoo removed. Ted asks her on a date but she says no due to it being unethical. Ted has ten sessions to convince her to change her mind.
Ted and Barney hit the town to celebrate St. Patrick's Day where Ted seemingly is rewarded for every bad behavior. Meanwhile, Lily and Marshall discover their apartment has even more problems... the floor is slanted.
Ted asks the dermatologist removing his butterfly tattoo on a date. The gang tries to talk Ted out of going out with someone he's going to see regularly (aka The Platinum Rule). Everyone shares their horror stories.
After everyone joins a gym, Barney sees Rhonda (the woman he lost his virginity to) there. After learning his performance with her was poor, he loses his confidence with women. He attempts to pick up models at a Victoria's Secret Fashion Show.
Ted thinks he finds the perfect woman (guest star Lindsay Price), but his friends all quickly notice a flaw in her that he missed. That gang soon reveals each others' flaws as well and point them out to each other.
Robin is dating a single dad and ends up forming a close bond with his son. However, when she decides the relationship is too serious, she needs to find a way to end her relationship with both the father and his kid.
When Robin shows up with a new boyfriend, Gael (guest star Enrique Iglesias), Ted decides he's ready to move on and hit the town with Barney. While out he meets Amy (guest star Mandy Moore), a tattooed party girl.
Barney: It's not possible! You cannot have sex on a windsurfing board! Lily: How do you know? Barney: Glad you asked, Lily. I have crafted a list of all vehicles, land-based, aquatic, and airborne, in which / on which it is possible to have sex. Of these 33, I have had sex in / on 31. Windsurfing board: not on the list. Oh, PS in order to hit 33, all I need is bobsled and the Apollo 11 space capsule. Lily: To get that last one, you'd have to break into the Smithsonian. Barney: This conversation never happened.