Season 3 Episode 2
"A Rock and a Hard Place Walk into a Bar"
Justin gets caught in the middle of a fight between Danny and Candace.
Now that Justin and Candace are dating, the whole gang is annoyed by their PDA and constant harmonizing - especially to the Grease soundtrack. Danny is especially peeved when Candace starts talking to his one-night stand about how she and Justin are taking it slow, and ends up convincing her not to sleep with Danny. So Danny decides to take out his anger on Justin, and they end up getting into a ridiculous karate-chopping fight that ends in Danny asking Justin to tell Candace to stop talking to his dates.
Despite Leslie's warning not to get involved, Justin talks to Candace, who then gets mad at Justin. Now Justin is stuck between his girlfriend and his best friend, who each claim he's on their side. In the end, he chooses not to take sides and instead lock himself in his office for eternity. Candace and Danny eventually make up and try to coax Justin out, but he refuses... until he hears them singing "Summer Nights" from Grease and he can't help but join in.