Michael Quinion’s treatment of the incipient libfix –tard (quoted from World Wide Words here, discussed on his affixes site here) omits what I believe to be by far the most frequent of the words with this libfix: the insult fucktard, defined in Sheidlower’s The F Word (3rd ed., p. 166) as “a despicably stupid person” (with cites from 1994 on).
Instead, Quinion picks celebutard as the “most common” of the words in this class, while admitting that it isn’t all that common. He also cites debutard, e-tard, lame-tard, scientard, conservatard, libtard/Libtard, and Avatard.
Why would Quinion have overlooked this item? Several possible reasons, not necessarily exclusive:
(1) Quinion is British, and fucktard might be heavily American: all of Sheidlower’s cites seem to be American; the many examples of fucktard you can google up are very predominantly American; and so, apparently are the sources of the 347 (!) definitions for the item in Urban Dictionary. So Quinion might not have noticed it.
(2) The examples that make it into print are mostly in reports of speech (in publications that allow fuck and words with fuck in them to appear in print); otherwise, the word appears in informal speech and writing (as in blogs). So Quinion might not have appreciated just how common fucktard is.
(3) The word is not only an insult, but a profane one, and Quinion might have left it off his list to spare his reader’s sensibilities. Certainly, some people are offended by it: Joe Clark reports to me that he “caused offence talking to a Canadian Oxford lexicographer about the word”. (A small irony here: The F Word is published by Oxford.)
Quinion is of course welcome to comment on fucktard and his treatment of it, and he probably will.
In any case, both parts of fucktard are understood non-literally (without reference to sexual acts or mental retardation), that is, as ritual insults.
Side note: googling on the word did pull up an instance of Fucktard McFucky, a type of Mc-naming pattern related to the ones mentioned briefly on Language Log in #5 here (the type X-y McXerson, as in Drinky McDrinkerson) and in #24 here (the type X-y McY, as in Drunky McPukeshoes), in the latter case referring to a wide-ranging discussion of jocular Mc-names on ADS-L in 2007.