That's like that old Jerry Sadowitz joke about Lenny Henry. The audience reacts to his statement like the above, and he says "no wait a minute, wait a minute, he IS a bastard, yeah? ..............and he's black". Whatever the context, there's no way to put those two sentiments together without sounding like a prick.He was specifically looking for a bastard that was black.
Because the colour of the rapist’s skin was black, hence ‘black bastard’
Am I wrong in thinking it's entirely deliberate? Who uses the word "cosh"? He's not a 1950's East End thug.