Dumb Ugly Cunt- it is a variation of DUFF
(Dumb Ugly Fat Friend)
The main difference being that a D.U.C. has no friends and is generally more bitchy- the DUC's bitchiness is enough to alienate her friends that already didn't care about her.
DUFFS travel as part of a flock where as DUC's fly alone
Carrie would be Lauren's DUFF except they're not friends any more so now she is just a DUC