It's Always Courtney, Courtney, Courtney! - S1.E24

Jen's hotter and more popular older sister Courtney comes to town, and the entire gang abandons Jen, with the guys astonished by Courtney's looks, and girls loving to listen about her life, ex-boyfriends, and trips abroad. But when Courtney takes the gang to a nightclub using a Fake ID, Jen is out to prove that she's more fun than her sister, but accidentally rips her dress while dancing, exposing her boobs.