an acronym for "Nigga is you serious?" It's a saying or a look you get when someone says something incredibly stupid or asinine. Something that make you wonder if their brain functions normally. Maybe they have a baby's brain.
Man #1: Yall ready to hit the club?
Man #2: Yeah dog, let's roll, tell your brother to come on.
Man #3: (walks out with a FUBU shirt on)
Man#1: NIUS!!!! We are leaving without you.