Basically, the Trickster shows up and puts them through a series of TV shows and commercials.
Dean meets Dr. Sexy (and swoons like a fan girl), Sam gets hit in the balls on a game show, and does a herpes cream commercial or something, the Trickster puts them in a sitcom where Dean's catchphrase is "Son of a bitch!", there's a cop show, and it's a pretty funny episode. Castiel keeps getting zapped away every time he tries to intervene.
The Trickster is my favourite. Ehe.