Abbreviation of "nah, nah, nigga". Allowing someone to know that in fact, they have it all wrong. While its meaning shifts based on the context, it is generally used as a retort following an incorrect statement, especially one made in jest.
Arthur: Man, what happened to rap after The Chronic? All downhill.
Lester: NNN, it's all good, Dre's still got it!
Rupert: Yo Leroy why was you actin like some kinda jive turkey at da club?
Leroy: NNN dat shit was on pointe. Bes respek.
Name names nigga. Originated in Yahoo African American Chat.
Quit talking shit if you refuse to NNN!
Noisy Nigger Neighbors
You've lived in an OK apartment for years, and then THEY move in. You've now got "Night of the Thumpasorus Peoples" over and over and over (or it could be daytime). If you ask them to turn down the bass, they'll say "hey, we're cool!" yet keep on doing it as if the conversation never occurred. You will always be the "complainer" and they will always be innocent victims of your "unreasonable" expectation that noise rules be obeyed. NNN is how ghettos begin.