Green’s Dictionary of Slang

(US campus) said of a boorish person.

1980		Eble Campus Sl. Fall 5: NC – person with No Class.
1996		Eble Sl. and Sociability 37: Two kinds of shortening reduce words to letters. The dominant type in college slang is initialism, which names the individual letters: [...] NC (no class) ‘a boorish person’.