Don,

One of the problems with "Political Correctness" is that it can be used to blur the boundaries of what is socially acceptable.

In terms of language, in my view a word or phrase ceases to be socially acceptable when its common usage become a derogatory term to describe a particular section of the community, or is deemed to vulgar for mixed company, whereas PC is much more patronising where 'polite society' deem a word of phrase could be potentially offensive.

I think as a society we have grown up in that racism is no longer acceptable in humour - but it is interesting that as racism decreased, vulgarity increased.