I grew up in St. Louis in an all-white neighborhood 1947-1965. "Cock" there meant female genitalia. I don't know why. It wasn't until I moved to Minnesota that I realized this usage wasn't universal. In those days, you never saw language like that in print, let alone in films, etc., and there was little contact between the races (that I was aware of, anyway) so there was no easy way to compare usage in one region/ethnicity with another.

I suppose things are changing now.