Gary Younge at the Guardian, a black journalist, reported stopping for directions in Mississippi and being threatened and told to move on. One might dismiss this as an isolated case, yet his friends subsequently told him that he was deranged to have tried it, and could have expected to be shot. "Driving while black" would appear to be the offence.
I cannot speak from experience, yet I suspect that the reality of Southern hospitality is actually quite circumscribed by race and appearance.