A non-negro nigga, or tripple N for short, is a person who is black even if not phenotypically appearing to me. Think Dominicans or white-passing lightskins
Bro 1: Bro I don't fuck with her. She uses the n-word.
Bro 2: Oh, dude it's ok, she's a tripple N.
Bro 1: What's that?
Bro 2: A non-negro nigga. Don't worry, she's black.