A campaign is under way to rebrand the US state of Kentucky as a place that "kicks ass". How did the once-profane term become so widely permissible?

It commands your attention like... well, a swiftly-directed boot to the rear.

There are those who might consider the phrase obscene. But in the United States, the verb to "kick ass" - like the adjective, "kick-ass" - is widely considered appropriate for general conversation.

Nowhere is this better demonstrated than in Kentucky, where a high-profile campaign has been launched to change the state's official slogan from "Unbridled Spirit" to "Kentucky Kicks Ass."

And why not, when both the current American president and his predecessor have happily gone on the record deploying the term?

The respectability of the phrase was surely confirmed by the 2010 superhero comedy Kick-Ass, set in New York, which was a hit in the US and beyond. A much-anticipated sequel is due for release later this year.

"If you can put it on the front of a movie theatre, you can say it out loud," says Paul Heacock, editor of the Cambridge Dictionary of American Idiom.

Derived from the British "arse", the US version is used widely and expressively to convey a range of sentiments.

"Kick ass" surely owes much of its popularity to the fact that it is so snappy and direct - an ear-catching, no-nonsense way to describe something that is vigorous and triumphant.

According to the Oxford English Dictionary, "to kick ass" is "to act roughly or aggressively; to be powerful or assertive".

But it is versatile enough to be applied to any bold course of action, or as a catch-all superlative.

A player could "kick ass" at chess by deploying an audacious opening manoeuvre. A florist might compose a "kick-ass" bouquet of chrysanthemums.

"As a phrase, it's quite malleable," Heacock says.

Image caption The Kentucky campaigners want to rebrand the state in a striking fashion

In Kentucky, the campaign to adopt the "Kicks Ass" slogan has attracted nearly 12,000 "likes" on Facebook.

According to Griffin VanMeter, one of the marketing professionals behind the rebranding push, the slogan was chosen to encapsulate the area's unpretentious dynamism.

"What it means to us is that instead of physically kicking someone's ass, it's evolved into a rallying cry that people can get behind," he says. "It's also a little risque which makes it that much better."

But not so risque that you couldn't wear it on a T-shirt, or display it on a bumper sticker.

Good manners remain highly valued across the culturally traditionalist south, says fellow campaigner Whit Hiler, but he says there have been only a few objections to the campaign.

"Kentucky is a fairly conservative state, we're in the Bible Belt," Hiler adds.

"But people aren't telling us 'You can't say that'. They're saying, 'Bring it on'."

It might be difficult to imagine, say, a British prime minister talking in such terms, but the phrase's entrance into the American mainstream has been confirmed by successive commanders-in-chief.

Asked by an interviewer during the 2012 Gulf oil spill whether it was time to "kick some butt" in order to solve the crisis, President Barack Obama ratcheted up the metaphor by replying that he would find out "whose ass to kick".

50 states, 50 slogans Just as each US state has its own officially designated nickname, flag, flowers and birds, so, too, does each have a slogan. They range from the strident (New Hampshire's Live Free or Die) to the aggrandising (Virginia Is For Lovers) and the surreal (Idaho's Great Potatoes. Tasty Destinations). According to Chekitan Dev, associate professor of marketing at Cornell University, they are "basically a competition between states to attract tourism dollars". One of the most successful is New York state's I Love New York, which - rendered in T-shirt form - has proved hugely popular with visitors and residents alike. Although he says he can see the logic of "Kentucky Kicks Ass" as a brash, in-your-face statement, Dev isn't sure it communicates much about what makes the state unique. "I think it would be more favourable from a resident's point of view," he says. "As a visitor, it makes me think, 'I don't want to go to Kentucky and get my ass kicked.'"

His predecessor, George W Bush, recalled in his memoirs how he resolved to find the perpetrators of the 9/11 attacks and "kick their ass".

But though the phrase may now be ubiquitous in popular culture, it was not always thus. Barely four decades ago, it was only rarely deployed in the mass media.

Green's Dictionary of Slang records the first published usage of the term in Nelson Algren's 1956 novel A Walk on the Wild Side, where a character declares: "I'm so tired of kicking asses I think I'll start crushing skulls."

However, Heacock notes that it only began to appear in print regularly from about 1975.

He believes it is no coincidence that this trend began shortly after the Watergate scandal, in which the White House was forced to release tape recordings of President Richard Nixon's profanity-strewn tirades.

"Before Nixon, you could pretend that people in high positions wouldn't use words that way," says Heacock. "That wasn't possible after 1975."

After this initial foray into the mainstream, Heacock observes that usage of "kick ass", "kicking ass" and "kick-ass" picked up even more frequently from roughly the year 1990 onwards.

But while in general taboos around swearing may have been relaxed over the same period, other terms still remain largely beyond the pale.

"'Kicking ass' is acceptable vulgarity," says Michael Adams, professor of English language at Indiana University-Bloomington and author of Slang: The People's Poetry.

"It's on the line but it's not stepping over the line."

It probably has its origins in the military, Adams says, where it was originally "kicking ass and taking names".

This longer version first appears in William Mares' 1968 book Marine Machine, a non-fiction account of a platoon's basic training, according to Jonathan Lighter's Historical Dictionary of American Slang.

You could argue that to say it's inherently wrong would be un-American Michael Adams, University of Indiana Bloomington

It's probable, Adams suggests, that the term was picked up by service personnel enlisted during World War II who carried on using it when they returned to civilian life, abbreviating it as they did so.

Sports coaches, in particular, found the jargon of the armed forces a useful motivational tool.

"It isn't as bad as some phrases because it has moved from the honourable profession of the military into sports," says Adams.

And because of the phrase's roots in two deeply-valued institutions, he adds, "you could argue that to say it's inherently wrong would be un-American".

"Kicking ass" is suggestive of the kind of rugged individualism lauded in American society since the era of the Wild West.

Coarse but not obscene, its informality absolves the speaker from any charge of cultural elitism, Heacock says.

"Plain speaking is something that Americans value," says Heacock. "It's a positive attribute."

As a result, politicians eager to prove they are in touch with the public have found "kicking ass" to be useful shorthand.

Obama and Bush no doubt both calculated that the phrase would make them sound strong, unpretentious and decisive, Heacock adds.

That one phrase can have such resonance says much about contemporary America.

While it may have taken decades, its journey from the barracks to the Oval Office comes as a short, sharp shock.

You can follow the Magazine on Twitter and on Facebook