Who doesn't love Courtney? Well, Hannah, for one. Number five on Hannah's list, Courtney is the pretty, sweet girl at school. But Hannah thinks she's a phony: Courtney only pretends to like Hannah when she needs something, like a ride to a party or an adventurous night of let's-catch-the-Peeping-Tom.
Courtney betrays Hannah by inventing a story that Hannah keeps sex toys in her dresser. Courtney's betrayal contributes to Hannah's belief that nobody around her is even slightly trustworthy.