Deandra "Sweet Dee" Reynolds is Dennis' twin sister and the main bartender at Paddy's.  Sweet Dee was definitely considered a loser in high school thanks in part to her back brace she had to wear back then.  Sweet Dee failed out of U Penn, where she studied psychology.  Now, she's mostly a failed actress and stuck as a bartender with her brother and his friends.

Deandra "Sweet Dee" Reynolds Quotes

Charlie: what is your spaghetti policy?
Dee: Are you hearing this? He doesn't belong in a place like this.

Frank: When it's white people, it's surviving. When it's black people, it's looting.
Dee: No Frank. It's because the white people are stealing bread and the black people are stealing speakers.

It's Always Sunny Quotes

Charlie: what is your spaghetti policy?
Dee: Are you hearing this? He doesn't belong in a place like this.

Mac: Fight Milk! The first alcoholic dairy based protein drink for bodyguards!
Charlie: By bodyguards! I drink it every morning so I can fight like a crow.