[It is, after all, a fair question. The OED has it at section 2 wherein sense a. deals with the abstract: morally unclean or impure; ‘smutty’ and launches it in 1599 with ‘No such blaspheming nor dyrtie speaking as before’. (Dirty words must wait till 1842 and the citations suggest ‘disreputable’ rather than obscene, i.e. ‘ “rejoin” is a dirty word down the Con. Club’. Perhaps an update will change things, but none of these examples suggest George Carlin’s micro-lexicon). As used of humanity, sense b. has ‘That stains the honour of the persons engaged; dishonourably sordid, base, mean, or corrupt; despicable.’ Those purveyors of ‘dirty words’, the world’s writers and publishers of pornography (and slang lexicographers?), will doubtless note the acknowledgement.
It is a useful catch-all, of course, but it did not, at least at first, catch all for whom it fished. The earliest case of a prosecution for publishing - that of scurrilous publisher Edmund Curll who in 1723-4 issued A Treatise of the Use of Flogging in Venereal Affairs and Venus in the Cloister, from a softcore French original - failed to hit its target. There were complaints, a prosecution was mooted, but obscenity law was there none. ‘This is filthy stuff’, intoned M’Lud, but there was no law under which Curll might suffer. No matter, the courts, not to be denied their prey, jailed him for libel. The bench returns in that well-known self-justification, originated in court and so beloved of the wowser both amateur and professional: ‘I cannot define pornography but I know it when I see it’, or, as paraphrased by the impious, ‘obscenity is whatever gives an old and impotent judge an erection.’]
In October 1973 the American comedian George Carlin recorded a 12-minute long monlogue in front of a live audience in a California theatre. In it he talked about the words ‘you couldn't say on the public airwaves, the ones you definitely wouldn't say, ever’. He then listed the words in question: fuck, shit, piss, cunt, tits, cocksucker, motherfucker, fart, turd, cock, twat and ass, then repeated them in a variety of colloquialisms. A few days later a New York radio station broadcast the monologue. A man who had been driving with his young son complained to the Federal Communications Commission (FCC). The FCC referred to its own regulations and stated the while the monologue was not obscene, it was certainly indecent and ‘patently offensive.’ The list, subsequently apostrophised as ‘filthy words’ remains a broadcasting touchstone.
The niceties of American law, and the fears of those who nanny US airwaves, are irrelevant here, but for the wordsmith, especially the slang collector for whom such words and their infinite synonymy are the very essence of professional life, there emerges an inevitable question. Are words, those agglomerations of neutral vowels and consonants, prisoners of human use and interpretation, ‘filthy’? Is there such a thing as an innately ‘dirty’ word? Do fuck’s four letters arrive as stained and stinking as the sheets on which it was lying? Is piss still dripping from some festering public urinal?
Let us consider the term. Dirty: ‘Not nice’, ‘nasty’, ‘unwholesome’, ‘insalubrious’ and of course ‘dirty’ as Roget has it. Synonyms being risqué, ribald, improper, indecent, indelicate, not for the squeamish; vulgar, coarse, gross; broad, free, loose; strong, racy, bawdy, Fescennine (no, I didn’t know: it’s either something to do with Fescennia in Etruria, famous for a sort of jeering dialogues in verse or with fascinus, Latin for a phallus-shaped amulet used to ward off the evil eye), Rabelaisian; uncensored, unexpurgated, unbowdlerized; suggestive, provocative, piquant, titillating, near the knuckle (what is this knuckle? that with which we perform the knuckle shuffle?), near the bone (and as for bone…); spicy, juicy, fruity; immoral, equivocal, nudge-nudge, wink wink; naughty, wicked, blue, off-colour; unmentionable, unquotable, unprintable; smutty, filthy, scrofulous, scabrous, scatological, stinking, rank, offensive; indecent, obscene, lewd, salacious, lubricious; licentious, pornographic; prurient, erotic, phallic, ithyphallic (lit. rendering one’s prick ‘straight’), priapic; sexual, sexy, hot. Those words, OK? Now wash your mouth out.
The idea of dirty as morally unclean and impure, or ‘smutty’ as the OED carefully defines it, is hardly new. The idea of ‘dirty speaking’ can be found in 1599; Ben Jonson savages a character as ‘dirty’ in 1637 and Sterne has a ‘dirty fellow’ in the Sentimental Journey. (Note 19th century slang’s arrive at the end of the Sentimental Journey, to have sexual intercourse; modern lit. crit. talks, presumably with tongue far from cheek, of an ‘open-ended end,’ the text simply makes it clear that our narrator retires to bed with a chambermaid). Rupert Brooke offers the earliest recorded citation for dirty stories in 1912 and adds dirty jokes a year later1. Maugham has dirty postcards in 1916, while dirty bookshops appear (surely only the dictionaries could be so laggard) in 1960. The dirty weekend is a coinage, but surely not an amusement, of 1969. Surprisingly, dirt as a noun has no place, at least on a morals rap, in the lexicon. Only do dirt on, with the perversely puritan D.H. Lawrence and his definition of porn as ‘doing dirt on sex’. So ‘dirty’ is all over the shop. Never more so than in the supposed ‘confessions’ of Mr. Patel’s top shelf where gorgeous, pouting slappers and their lubricious (if imagined) exploits, are routinely paraded as ‘dirty’. The use, I assure you, is not pejorative. Paradoxically it is only in slang, where all these ‘dirty’ words abound, that ‘dirty’ is quite devoid of sexual content. Here at least the word can actually mean bad, terrible or objectionable, or, in a tradition that has continued since the 16th century’s rum meant good to villains and bad to the respectable, good, wonderful and excellent. It refers to the possession of or addiction to drugs or the holding by criminals of incriminating evidence; it can mean rich or at least comfortable. In phrases such as dirty great it works to intensify; in Australia it means resentful. None of which even ponder on sex.
But then you start thinking. ‘Dirty . . .words’. I mean tell me, what are we on about here? Words have no substance. No dimension, other than conceptual, no depth, no width, no dusty corners, no nooks and crannies wherein such filth may hide. So what are we talking about? Lenny Bruce used to do a ‘bit’ in which, accused of telling ‘dirty toilet jokes’, he pondered on the literal meaning of the phrase, railing against the mute porcelain, before ‘I’d thunder out of the bedroom and dash open the door and . . . “Look at you, you dirty, dopey, Commie toilet, you! And the tub and the hamper – you should know better.”’ OK, it’s all metaphorical, and once you do take this stuff too literally you’re hand-in-glove with the morons for whom the pursuit of ‘dirt’ is an apologia for their gruesome vitae, but words, even the most excoriated, are not of themselves dirty
What they can be is highly apposite. Why has fuck lasted the course since its first sightings six centuries ago? Because it works. Swive didn’t make it, jape fell away (outside the world of Jennings and Billy Bunter – and does such a usage cast new light on those dormitory romps?), sard has been lost for years (though there was once ‘teach your grannam to sard’, which preceded teaching her to ‘suck eggs’). But fuck makes it. Rooted most probably in the Latin pugnare, to fight (thus parent to that ever-expanding list of terms that mate sex with violence), and satisfactorily echoic of the slap of copulatory flesh, it does the biz. Is cunt ‘dirty’? Cunt comes from cwm, redolent in its native Welsh of streams and valleys. These days they’re probably polluted, but not morally. Turd means torn (as in from the body). OK, shit, which comes from the Anglo-Saxon scite, means dung and yes, I wouldn’t deny the dirt here. Physical, though, not mental. But cock relates to a cockerel plus the cock’s head seen as a tap-like shape, this secondary aspect emphasized by its function in ‘pouring’ semen (or urine), tit from teat, twat from the dialect twitchel, a narrow passage, prick began life as a female term of endearment for the (male) beloved, and so on and so forth. Half the goddam stuff was standard English anyway until the missionaries of repression began weaving their sick webs over 19th century language.
Is sex dirty, as Woody Allen has famously asked? Depends what you mean by dirty, really. One man’s spiked heel, G-string, white thigh and black stocking is another woman’s . . . other woman. Far be it from me… But words, those I do know. And are words dirty? If I may choose the mot juste – bullshit.
It’s always older than you think: a cursory search of newspaper databases puts the jokes back to 1839 (though it may be that dirty here means ‘mean’ or ‘unkind’); dirty story was used, told in a wedding speech and alongside a ‘smutty song’, in 1811. Dirty postcards appear in 1902, but this may refer to the sender’s words; the picture appears from 1909. Dirty bookshop predates to 1955, but further research may well improve this
I hope this is an OK place to leave you a pointer for your dictionary, for the entry on "skinny" n.3:
There have been some recent discoveries on "the skinny" (i.e. information) announced on ADS-L, connecting it to U.S. Naval Academy slang, where "the skinny" meant physics and chemistry classes (after a notably skinny professor in the 1860s, it's claimed). Apparently this shifted from facts/knowledge of physics to facts/knowledge of anything. You can see some of the quotes illustrating the transition at ADS-L: August 2019, September 2019, July 2022, September 2022. Also see an article on "the skinny" by Gerald Cohen in Comments on Etymology, April 1998.
At any rate, it's pretty clear that it originated in the US military; you can verify that in Google Books (look also for "straight skinny"), since military sources are predominant until at least a decade or two after WWII.
More links and quotes posted at Wordorigins.org, discussion thread "skinny":
https://dwilton.discussion.community/post/skinny-10513436?pid=1334180061
This reminds me of John Waters's bit where he said you ought to wash your hands after shaking hands, rather than when you go to the bathroom, because your penis isn't touching dirty doorknobs, and should be cleaner than your hands if you showered that morning...