I got into a heated discussion about this once in the BART forum.
I explained it then but I'll give you a short touch.
I can't really speak on the rest of the Yay but I can speak on EPA.
EPA used to be a predominately Black city.
There were a few Mexicans and Poly's around the time I started living here. Non-blacks picked up on many things from the blacks, including their slang. Before I knew it, everyone used the word "nigga" like nothing.
Nigga and "rogue" to be exact. It was part of our vocabulary, black cats would reffer to us as "niggas" so everyone picked up on it. Next thing I know, the entire West Bay started using the word, no matter what color you were. Cats in the East Bay and in the South Bay don't use it as much.
But I guess the same happenned with everyone else, it became part of our Bay slang.
Hell even a Fillipino cat here at work tells me says it.
And he just moved here from Long Beach where he says everyone down their uses it.
I ain't gonna lie, I use it all the time.
It's how we grew up ya know?
A few black cats trip on it, but they got issues.
All of my folks ain't got a problem with it.
I can't help it, I use it even in our music.
But I'll think twice about it cuz I know there's cats out there that are new to this....