2.An extremely attractive woman, one you would love to fuck, when the emphasis is placed on 'not' rather than 'fat'.
3.A girl who's only redeeming attribute is that she is not fat.
Man 2: "Yeah, why not, she's not fat"
2. Man 1: "Woah, she is NOT fat!"
Man 2: "Yeah, she's stunning"
3. Man 1: "I can't believe you fucked her! She's rough as guts!"
Man 2: "I know but she's not fat"