frump·mon·ster
n.

Root: Derived from the words 'frump,' meaning 'very plain and unfashionable' and 'monster,' meaning 'a grotesque beast.'

Definition: A person, usually a female, who is excessively frumpy and gross. (i.e.: wears out of date fashions, very homely, clothes don't fit her well, doesn't know what looks good and what doesn't, shops at Wal*Mart, etc...)