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The logic of your post is flawed and your assumptions, untenable.
You write: "However, the fact that it caused upset shows that it wasn't just a joke. It's the truth or a perception they wish to convey but which needs to be disguised or softened in the delivery".
An "offensive" comment is not necessarily the truth or perception someone wishes to convey, but which needs to be disguised. The joke teller often has no idea the comment is "offensive" (as opposed to a "sexist" who knows she/he is making an offensive comment and who then tries to hide behind 'it's only a joke').
The egregious part of your post is the first part of the quote above - "However, the fact that it caused upset shows that it wasn't just a joke". The point is that if someone is 'upset' by an 'offensive' comment, the current implication is that the upsetter or offender is to blame, with no further questions asked.
That doesn't sit well with me at all. In Australia where people can choose their number plates, someone had a number plate 'kookie'. Apparently this is a vulgar term for a vagina, in some Asian language (I forget which), and an Asian lady took offense and complained. Sorry. Just too wide. There is nothing in law (nor should there be) which seeks to protect people from offence.
Otherwise it's just too easy - I am offended by your post.
Your post is a truth or perception you wish to convey but which needs to be disguised or softened as fair comment.
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