"The General is sorry to be informed that the foolish, and wicked practice, of profane cursing and swearing (a Vice heretofore little known in an American Army) is growing into fashion; he hopes the officers will, by example, as well as influence, endeavour to check it," George Washington wrote to his troops in 1776.

Mohr writes that many swear-phrases we use today got their start in Medieval Europe, when the Bible provided the basis for swearing oaths -- something people thought God asked of his followers in the Old Testament. (It's where we got the "holy" in "holy shit," for example).

But expletives predate even the spread of Christianity: The Romans' mouths were incredibly dirty, and many of their taboos were ones Westerners still hold today.

"Speaking with Roman plainness," as the euphemism for cursing at the time went, mostly involved vividly describing genitals, which were considered both shameful and awe-inspiring -- veretrum and verecundum -- Mohr found. The ten worst words in ancient Latin centered on bodies and sex. Slight a Roman, and he might retaliate by threatening to perform irrumatio, or oral rape.

Most Roman obscenities were hurled as insults, but like in Medieval Europe, they sometimes had a religious role, as well. The Gods, it seems, sometimes liked it when mere mortals cursed like sailors. Mohr writes:

Obscenity made some religious rituals succeed, though, too. Obscene words could please gods such as Priapus, with his enormous, perpetually erect phallus, and were thought to promote fertility and to protect against the evil eye. In ancient Rome, in other words, the Shit itself could be Holy.

Interestingly, many of these Roman swears weren't passed down to English. The Latin cunnus isn't even the predecessor of our see-you-next-Tuesday. "Latin usually gives us our proper medical terms for immodest parts of the body-- vagina and penis, for example," Mohr writes. "Not our primary obscenities."

The Romans did, however, employ their own c-word frequently -- in graffiti and even in poems -- but often to refer to the body part itself, not as an insult. In one epigram, the poet Martial rhetorically asks an old woman why she's plucking her pubic hair, inquiring, among other things, "Why stir up the ashes in your tomb?"

"Fuck," or futuo, was also not always pejorative. One Pompeian offered this tender sentiment to a friend: "Fortunatus, you sweet soul, you total fucker!"

Instead, another word was considered far more foul: landica, or clitoris. Mohr explains why:

People swear about what they care about, and the Romans cared about the clitoris. They thought that both male and female partners in intercourse had to achieve orgasm for conception to occur, a wrong, but gallant, idea.

Other Roman expletives centered on passivity and aggressiveness in sex -- passivity being considered far inferior. There were two profanities for a man who allowed himself to be penetrated -- catamitus and cinaedus -- and the sure-fire way to spot a cinaedus was that he "scratched his head with one finger." Some think it was the middle finger, which even back then was offensive for its perceived resemblance to an erect member. The worst of the worst insults related to being on the receiving end of oral sex, since the mouth was the most sacred of body parts.