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.

You are not eating a hoagie. You are just jamming meats and cheeses in your mouth.

Dee [to Frank]

It's Always Sunny Quotes

Dennis: I am having feelings again. Like some kind of fourteen year old kid. You remember, feelings right?
Mac: Yeah. I have feelings every single day of my life.
Dennis: Do you?
Mac: Are you saying you don't have feelings?
Dennis: What I'm saying is a built up a shell.. a shell around myself. A cold, calculated shell that couldn't be broken by anything but marriage.

Let's pull up our bootstraps, oil up a couple asses, and do a little plowing of our own. POW! (gestures a fist punch up an invisible ass)... Not gay sex.

Mac