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

Dennis: It's because of those bison fingers.
Dee: I do not have bison fingers!
Frank: Yeah you do. Your mother had to have a c-section because of those hands.

Dee: Who slams a door?
Frank: Babies.
Dennis: That guy has some real growing up to do. Have some repect for Christ's sake... I am legend.

It's Always Sunny Quotes

Frank: I opened up to a therapist just once. I was a kid. I got into a fight. The doctor asked me question after question, got me so scrambled up. Next thing I know, I was shanghai'd upstate to a nitwit school. You know what a nitwit school is?
Therapist: I assume you mean a school for the mentally disabled.
Frank (spits pistachio shell): Yeah, not just for nuts in the head, but bodies, too. Back then science was real crude, they stuck us all together. My roommate was a frog-kid. You ever see a frog-kid?

No I don't eat dragon, cause, uh, it's not a meal for peasants, it's a meal for kings, and I'm sort of a common man. But they don't eat us, it's a common misconception. They actually eat gold and treasure -- that's why they're always sitting on a pile of it.

Charlie