A woman who is, or appears to be, a paragon of sluttitude, by the way she dresses, behaves, or both.
An uberslut, or a girl who just looks like one.
That girl over there with the whaletale is such a slutwich. I bet she'd blow you after one beer.
Nadya has no figure so she has to dress like a slutwich to satisfy her obsessive need for attention from men. In reality, she is a total prude.