Rowan Pelling: This way, ladies. If there are any...

I blame Chris de Burgh; ever since he indelibly associated the word lady with highlights, garish frocks and slow-dances at provincial discos the species has been on a hiding to nothing.

But it wasn't always thus. I was once told a joke that seems to me to summarise every nuance the English language can possibly invest in the term "ladylike": when a diplomat says yes, he means maybe; when a diplomat says maybe, he means no; and when a diplomat says no, he's no diplomat. When a lady says no, she means maybe; when a lady says maybe she means yes; and when a lady says yes, she's no lady.

A lady is is, in short: modest, decorous, courteous, tactful and refined. She is the antithesis of coarse. If you can easily imagine a woman belching, farting, swearing, licking her plate, sporting a tattoo or piercing, drinking to excess or fornicating, she's no lady.

Once upon a time, of course, the bar would have been higher: a lady would have been required to demonstrate a comprehensive grasp of etiquette, deportment, small talk, flower arranging, cordon bleu cooking, and household management. Naturally she should also have known how to disembark from a sports car while looking soignée.

Nowadays the definition is edging ever closer to the cast-iron certainty that you will never see said female collapsed on the pavement in a pool of her own vomit, marketing her home porn movie on the internet, or flaunting her shaven chuff as she falls out of a stretch limo. All of which makes it increasingly hard to identify any bona fide ladies in public life. But this week's G20 summit has thrown up a few possibilities.

The self-possessed Sarah Brown has never put a foot wrong in public and manages to be loyal and low-key while avoiding any whiff of little-woman servility. The vivacious Michelle Obama is less self-effacing, but has the innate grace and charm that invests the moniker First Lady with real meaning.

These women manage to fly the flag not just for their respective homelands, but for the very concept of gentility, combining accomplishment and intellect with likeability. A near-impossible task to pull off, as Cherie Blair and Hillary Clinton could ruefully testify.

Poor Cherie was a wee bit déclassé and quite frankly it suited her: she was at her cheerful best when she sang Beatles' songs out of tune, or ligged a stay in Cliff Richard's mansion. And the more the spin doctors groomed and primped poor Hillary, the more vividly you imagined her wearing boxers and smoking cigars in private. You can't be a lady and a hard-ass bitch.

But in this age of mass-market fakes you must beware the counterfeit lady. Take Carla Sarkozy: butter wouldn't melt in her mouth as she sports demure pumps and Christian Dior couture. But the pouting nude photos from her modelling days tell another story entirely. As the new publisher of The Lady says defiantly: "The Lady is greater and grander than sex."