Lex acknowledged that the acronym was pejorative, but said it contained “much truth” and went on to play with words, saying that pigs which previously flew had now fallen to earth.

Perhaps it was the light-hearted tone which gave some people a pretext to take offence. Others had used the expression without upsetting anyone. The Daily Telegraph quoted it in a report by the French bank BNP-Paribas in May; Newsweek used it for a headline on July 14.

But, as Obama found, it can be unwise to make jokes using the name of animal which is traditionally (though unfairly) regarded as dirty and impure in most cultures.The Democratic candidate for the US presidency charged his Republican opponent John McCain with putting “lipstick on a pig” – a metaphor for disguising unattractive policies to make them appealing to voters.

This colourful expression has been a favourite of investment and real estate brokers for several years. The Wall Street firm Charles Schwab used it in a 2002 television spot insinuating that a rival was capable of dishonest advertising. An executive was shown telling younger colleagues: “We've got a lot of stock to move. Tell your customers it's red-hot … Just don't mention the fundamentals—they stink. There are a couple of courtside playoff tickets for today's winner." He pauses. "Now let's put some lipstick on this pig. Get to work, people."

Books by an American management consultant, Mark McGlinchey, and by Victoria "Torie" Clarke, a public relations consultant who has served under three Republican US presidents, echoed the phrase in their titles.

A brief Google search produced dozens of similar quotations from Forbes, the Wall Street Journal, Bloomberg and other media specializing in financial news. McCain too recently accused the Democrats of putting lipstick on a pig. None of which stopped his campaign managers from asserting that Obama had clearly meant to insult McCain’s running mate, Sarah Palin, the governor of Alaska. Had not Palin – a sports and hunting enthusiast – touted her macho credentials by declaring that lipstick was the only difference between herself and a pit bull terrier?

But it is one thing to compare yourself to an attack dog and another thing to claim that someone else has likened you to an inoffensive farm animal.

The pig is associated in colloquial English not only with dirt but also with personal defects in humans – and not just policemen and male chauvinists.We call obstinate people pig-headed and aggressive drivers road hogs; lazy or incompetent craftsmen are said to make a pig’s ear of a job; a conman might try to sell you a pig in a poke or to convince you that pigs can fly; gluttons pig out; the undeserving rich live high on the hog – or on the pig’s back in Australia, where implausible claims are dismissed as “pig’s arse”.When US politicians accuse one another of wasting public money to keep local lobby groups happy they refer to pork-barrel politics.

It is probably too early to tell whether Obama has been badly hurt by using the expression.And Palin’s claim may yet come back to haunt her if women voters see her as a lipstick feminist, a woman who see no contradiction in calling herself feminist while using sexual allure to gain power over men.