When no longer wearing his trademark suits, Barney wears a shirt depicting the cover of the book "Die Neue Wohnung" (german for 'The new appartment') by famous architect Bruno Taut, indicating that the shirt might actually belong to Ted. Barney probably took all his "new" non-suit clothes from Ted's more casual wardrobe.
This is the show's 100th episode.
According to the DVD commentary of this episode, there was a scene where the suits moved and talked to Barney in different accents. It was cut out because of the 18 minute limit they had due to the song at the end being 3 minutes long. You can see a suit move at the end of the episode, it was going to be a follow up to this.
The music accompanying Barney's hidden suit in the restroom in MacLaren's pub is "Bullwinkle pt. II." A reference to a scene in Pulp Fiction (1994). Where, to the same song, Vincent Vega (John Travolta) shoots up heroin.