I got myself a copy of Tolkien's 'Letters' at the Tolkien Thing. A fascinating read that gives a lot of background. Just this moment I stumbled over this one. Here's to you, fanficcers!
(The letter is from 12/12/1966 to publisher Allen & Unwin, about a proposed sequel to LotR, written by a fan.)
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"Dear Mrs Hill,
I send you the inclosed impertinent contribution to my troubles. I suppose that since one cannot claim property in inventing proper names, that there is no legal obstacle to this young ass publishing his sequel, if he could find any publisher, either respectable or disreputable, who would accept such tripe.
I have merely informed him that I have forwarded his letter and samples to you. I think that a suitable letter from Allen & Unwin might be more effective than one from me. I once had a similar proposal, couched in the most obsequious terms, from a young woman, and when I replied in the negative, I recieved a most vituperative letter.
With best wishes,
Yours sincerely,
J.R.R.Tolkien"
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I'm almost sure that Tolkien, well-mannered gentleman that he was,uses 'ass' in the meaning of 'donkey' here.
We can only be grateful that he never made it into the age of internet and saw himself confronted with hoardes of young and not so young women writing fanfiction about the asses of his protagonists (not donkeys). And Mary Sues, of course.
By the way, this nasty letter by a budding fanficcer must be also counted as the first Fandom Wank in Tolkien fandom history! Whee!