While looking for something else entirely, I stumbled upon an etymological reference in Dictionary.com that was more than a bit surprising to me. Under the word kiss it notes, towards the end, “Insulting invitation kiss my ass dates at least from 1705, but probably much older (cf. “The Miller’s Tale")."
I am inferring from the absence of quotation marks around “kiss my ass” that the etymologer(s) responsible for this comment are not necessarily suggesting that the specific turn of phrase “kiss my ass” is of such antiquity. And, indeed, the dictionary.com entry for “ass” indicates that the term, as used to refer to a person’s backside, is an originally nautical term that is “first attested” to in 1860, although it notes that the slang term may be much older than that, particularly if Shakespeare’s naming of the character Nick Bottom (who literally becomes an ass) is the pun that many suppose it is. Although it seems to me that there is a difference between punning on arse/ass and donkey/bottom, and actually using the word ass, in a non-punning context, to refer to one’s bottom.
IIRC, “The Miller’s Tale” involves a scene in which a bottom is literally (and inadvertently, at least by the kisser) kissed, but nobody actually says anything remotely similar to “kiss my [bottom]” in that work.
I would have guessed that the term, “kiss my [bottom]”, was quite modern, even if an older term for bottom than “ass” is used (such as “arse"). Certainly, if I had attempted to write a historical novel set in 1705 or earlier (something I am unsuited to do for a variety of reasons) I would have instinctively steered clear of seeming modernisms like “kiss my ass/arse.” But a quick google search turned up the poem “Mac Flecknoe”, a satire by Dryden dating to 1682, which mocks another writer, Shadwell, for, among other things, using the phrase “kiss my arse” in one of his plays, which, per Dryden, reduced it “...to a farce.”
So, there you have it: one more example of my untested intuitions about the relative recency of a turn of phrase turning out to be wildly inaccurate. It’s hardly news that such things are unreliable, but hopefully this example is at least mildly interesting, or at least amusing, to others on this forum.