From Mother Tongue - English & How It Got That Way by Bill Bryson:

SWEARING

AMONG THE CHINESE, TO BE CALLED A turtle is the worst possible taunt. In Norwegian, devil is highly taboo-roughly equivalent to our fuck. Among the Xoxa tribe of South Africa the most provocative possible remark is hlebeshako "your mother's ears." In French it is a grave insult to call someone a cow or a camel and the effect is considerably intensified if you precede it with espece de ("kind of”) so that it is worse in French to be called a kind of a cow than to be called just a cow. The worst insult among Australian aborigines is to suggest that the target have intercourse with his mother. Incest is in fact so serious in many cultures that often it need be implied in only the vaguest terms, as with tu madre in Spanish and your mama among blacks in America. Often national terms of abuse are nonsensical, as in the German schweinehund, which means "pig-dog."

Some cultures don't swear at all. The Japanese, Malayans, and most Polynesians and American Indians do not have native swear words. The Finns, lacking the sort of words you need to describe your feelings when you stub your toe getting up to answer a wrong number at 2:00 A.M., rather oddly adopted the word ravintolassa. It means "in the restaurant."

But most cultures swear and have been doing so for a very long time. Dr. J. N. Adams of Manchester University in England studied swearing by Romans and found that they had 800 "dirty" words (for want of a better expression). We, by contrast, have only about twenty or so, depending on how you define the term. The Rating Code Office of Hollywood has a list of seventeen seriously objectionable words that will earn a motion picture a mandatory R rating. If you add in all the words that are not explicitly taboo but are still socially doubtful-words like crap and boobs-the number rises to perhaps fifty or sixty words in common use. Once there were many more. More than 1,200 words just for sexual intercourse have been counted.

According to Dr. Adams's findings, certain things have not changed in 1,500 years, most notably a preoccupation with the size of the male member, for which the Romans provided many names, among them tool, dagger, sickle, tiller, stake, sword, and (a little oddly perhaps) wonn. Even more oddly, the two most common Roman slang words for the penis were both feminine, while the most common word for female genitalia was masculine.

Swearing seems to have some near-universal qualities. In almost all cultures, swearing involves one or more of the following: filth, the forbidden (particularly incest), and the sacred, and usually all three. Most cultures have two levels of swearing-relatively mild and highly profane. Ashley Montagu, in The Anatomy of Swearing, cites a study of swearing among the Wik Monkan natives of the Cape York Peninsula. They have many insults which are generally regarded as harmless teasing-big head, long nose, skinny annsand a whole body of very much more serious ones, which are uttered only in circumstances of high emotion. Among the latter are big penis, plenty urine, and vagina woman mad.

English is unusual in including the impossible and the pleasurable in its litany of profanities. It is a strange and little-noted idiosyncrasy of our tongue that when we wish to express extreme fury we entreat the object of our rage to undertake an anatomical impossibility or, stranger still, to engage in the one activity that is bound to give him more pleasure than almost anything else. Can there be, when you think about it, a more improbable sentiment than "Get fucked!" We might as well snarl, "Make a lot of money!" or "Have a nice day!"

Most of our swear words have considerable antiquity. Modern English contains few words that would be unhesitatingly understood by an Anglo-Saxon peasant of, say, the tenth century A.D. but tits is one of them. So is fart, believe it or not. The Anglo-Saxons used the word scitan, which became shite by the 1300s and shit by the 1500s. Shite is used as a variant of shit in England to this day.

Fuck, it has been suggested, may have sprung from the Latin futuo, the French foutre, or the German ficken, all of which have the same meaning. According to Montagu the word first appears in print in 1503 in a poem by the Scottish poet William Dunbar. Although fuck has been around for centuries, possibly millennia, for a long period it fell out of general use. Before 1503, the vulgar word for sex was to swive.

Pussy, for the vagina, goes back at least to the 1600s. Arse is Old English. Common names for the penis, such as dick, peter, and percy (used variously throughout the English-speaking world), go back at least 150 years, though they may be very much older. Jock was once also common in this respect, but it died out, though it survives in jockstrap.

It is often hard to trace such terms reliably because they weren't generally recorded and because they have, for obvious reasons, seldom attracted scholarly investigation. Buttocks, for instance, goes back to at least the thirteenth century, but butt, its slangy diminutive form, is not recorded until 1859 in America. As Stuart Berg Flexner observes, it seems highly unlikely that it took 600 years for anyone to think of converting the former into the latter. Similarly, although shit has been around in various forms since before the Norman Conquest, horseshit does not appear before the 1930s. Again, this seems improbable. The lack of authoritative guidance has sometimes encouraged people to come up with fanciful explanations for profanities. Fuck, it was suggested, was originally a police blotter acronym standing for "For Unlawful Carnal Knowledge." It is nothing of the sort.

After O. K., fuck must be about the most versatile of all English words. It can be used to describe a multitude of conditions and phenomena, from making a mess of something (fuck up) to being casual or provocative (fuck around), to inviting or announcing a departure (fuck off), to being estimable (fucking-A), to being baffled (I'm fucked if I know), to being disgusted (fuck this), and so on and on and on. Fuck probably reached its zenith during the Second World War. Most people are familiar with the army term snafu (short for "situation normal-all fucked up"), but there were many others in common currency then, among them fubar (''fucked up beyond all recognition") and fubb ("fucked up beyond belief').

Piss goes back at least to the thirteenth century, but may be even older. It has been traced to the Vulgar Latin pissiare and thus could conceivably date from the Roman occupation of Britain. As piss became considered indecent, the euphemism pee evolved, based simply on the pronunciation of the first letter of the word. In America, piss has been documented since 1760 and pee since 1788.

The emotional charge attached to words can change dramatically over time. Cunt was once relatively harmless. Chaucer dropped it casually and severally into The Canterbury Tales, spelling it variously queynte, queinte, and even Kent. The City of London once had an alley favored by prostitutes called Gropecuntlane. It was not until the early eighteenth century that the word became indecent. Shit was considered acceptable until as recently as the early nineteenth century. Prick was standard until the eighteenth century. Piss was an unexceptionable word from about 1250 to 1750, a fact still reflected in the common French name for urinals: pissoirs. On the other hand, words that seem entirely harmless now were once capable of exciting considerable passion. In sixteenth-century England, zooterkins was a pretty lively word. In nineteenth century England puppy and cad were highly risque.

Today the worst swear words in English are probably fuck, shit, and cunt. But until about the 1870s it was much more offensive to be profane. God damn, Jesus, and even Hell were worse than fuck and shit (insofar as these things are quantifiable). In early swearing religion played a much more prominent role--so much so that in the fifteenth century a common tag for Englishmen in France was goddams. Swearing by saints was also common. A relic of this is our epithet by George, which is a contraction of "by St. George" and has been around for centuries. Cock was for a long time not only a slang term for penis but also a euphemism for God. Thus in Hamlet Ophelia could pun: "Young men will do't, if they come to't; By cock, they are to blame." Some of these were surprisingly explicit-"by God's bones," "by God's body"-but as time went on they were increasingly blurred into more harmless forms, such as zounds (for "God's wounds"), gadzooks (for "God's hooks," the significance of which is obscure), and God's bodkins or other variants like odsbodikins and gadsbudlikins, all formed from "God's body."

This tendency to transform profanities into harmless expressions is a particular characteristic of English swearing. Most languages employ euphemism (from the Greek, meaning "to speak well of') in some measure. Germans say the meaningless Potz blitz rather than Gottes Blitz and the French say par bleu for par Dieu and Ventre Saint Gris instead of Ventre Saint Christ. But no other language approaches English for the number of delicate expletives of the sort that you could safely say in front of a maiden aunt: darn, durn, drat, gosh, golly, goodness gracious, gee whiz, jeepers, shucks, and so on. We have scores, if not hundreds, of these terms. However, sometimes even these words are regarded as exceptionable, particularly when they are new. Blooming and blasted, originally devised as mild epithets, were in nineteenth-century England considered nearly as offensive as the more venerable expletives they were meant to replace.

But then of course the gravity of swear words in any language has little to do with the words themselves and much more to do with the fact that they are forbidden. It is a circular effect. Forbidden words are emotive because they are forbidden and they are forbidden because they are emotive.

A remarkable example of this is bloody in England, which to most Britons is at least as objectionable a word as shit and yet it is meaningless. A number of explanations have been suggested, generally involving either a contraction of an oath such as "by Christ's blood" or "by our Lady" or else something to do with menstruation. But there is no historical evidence to favor one view over the other. The fact is that sometime around the sixteenth century people began to say bloody and to mean a curse by it. It's now often hard to tell when they meant it as a curse and when they meant it to be taken literally, as when in Richard II Richmond says, "The bloody dog is dead."