If she acting like a bitch, I guess we're around white folk
The line is playing on the concept that upper/middle America is uncomfortable with urban behavior, which is typecast as aggressive and less civilized. Big Boi’s stating that if her actions are interpreted as being bitchy, it is probably because there are white folks around to see it that way.
She may have actually altered her personality to fit in with the white folks and he’s calling her out on it.
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