NUF is an abbreviation of Novel Update Forum. Novel update is a site that gives links to other sites with English (often illegal/unauthorized) Translations of Asian Novels. If you read this in a chat this might be what the person means.
A slut that should just stop and sit her ass down in a corner and clean her schedule! A nuf nuf usually are the ones that wear short shorts to an ice skating rink and the tightest of dresses to school.
"Ew, look at that girl! Who wears shorts to an ice rink?!"
"She's just a nuf nuf."