I don't think political correctness and direct insults have anything to do with one another. "Politically incorrect" implies that some people may find a word offensive while others do not. "Negro" is no longer politically correct, but it's not usually spoken as a direct insult. "Wanker" is intended as an insult. Asking whether "wanker" is politically correct is a bit like asking whether "Goddamned shit-for-brains fuck-faced asshole" is politically correct.