GFUC is an acronym for Good Far, Ugly Close.
This pertains to a situation where a person seemingly looks attractive from a far distance, from either the front or the back, but in reality, up close, the person is not attractive.
Person 1 to Person 2: "Hey yo, look at that fine ass girl over there!"
-girl walks by-
Person 1: Never mind yo, she's a GFUC.