It originates from "What's good?" which at the time it was coined was like another way of saying hello. It evolved into a hostile inflection to suggest to someone that something they did caused offense. This then evolved into "What's REALLY good?!" which then was substituted for what's really hood, basically meaning "if there's a problem we can solve this like they do in the hood." Likely the etymology of this phrase has something to do with the phrase "what's poppin'?"
Use "what's really hood" with EXTREME CAUTION.
1. Yo, what's really hood muh nigga?
2. Nothing, it was a mistake!
1. You damn right it was! *pulls out a gun*
2. Calm down, that's uncalled for..
1. -person one is too high/doped up/coked up to use reason. He murders person 2 and later put in jail for 30 to life-