Katy Guest: Boris's charm is an acquired taste at best. It makes me sick

It's more baffling than the Large Hadron Collider. More nauseating than the "walls of fat" being scraped from London's sewers. The summer news story that has everyone bringing up breakfast this weekend is as predictable as it is inexplicable. It fills me with more impotent fury than if every tourist on the London Tube simultaneously stopped dead right in the doorway to the Circle Line.

Once again, London is abuzz with the question: "Would you have sex with this man?" And, of course, the answer: "I wouldn't touch him with yours, mate."

The news concerns Boris Johnson, his "close friendship" with a Belgravia socialite, and the fact that she split from her long-term partner when her baby popped out looking uncomfortably like a tiny bawling clone of the London Mayor. Imagine the lady's surprise (her friends reported) when a DNA test showed that her partner is not the father of her child. "Mr Johnson never talks about his private life," said his long-suffering spokesman.

This could be because the Mayor's private life resembles a particularly low-rent episode of The Jeremy Kyle Show – one in which, uniquely, there is a man on stage more odious than Jeremy Kyle. "Put something on the end of it!" the host would yell, to jeers and boos from the audience, while Boris slumped, legs akimbo, surrounded by snivelling women.

Should Boris turn out to have anything to do with the strange affair at Belgravia, it would not be the first time that he has had unprotected extramarital sex with an unsuspecting popsy who was obviously busy riding polo ponies when the rest of us were learning about contraception.

His affair with colleague Petronella Wyatt ended in tears and an abortion clinic. He was bewildered when one mistress turned down his invite to join him on holiday with his wife and children. He took up with his current wife, Marina Wheeler, while still with his last, Allegra Mostyn-Owen. In 2006 he refused to deny an affair with the journalist Anna Fazackerley...

Any woman who does it with Boris must by now know what she is getting. There are those who say that he has a certain je ne sais quoi, but fortunately that can be cleared up these days with antibiotics. But let's not denounce Boris's philandering merely on the grounds of his looks (though he does have that strangely repellent translucent marshmallow skin that is unique to a certain type of indoor-reared posh boy and which is so queasily redolent of milk-fed veal). Rather, it is his attitude that makes him sickening.

This is a man who thinks that rules are only for the little people – something that he presumably learned in the Bullingdon Club. A representative of modern London who jokes about "flag-waving piccaninnies" with "watermelon smiles". An ambassador for Britain who slouches through the Olympic handover ceremony, hands in pockets, ignoring the Beijing mayor. He was asked by officials to do up his jacket out of respect, he later bragged, but he thought, "sod it".

Last week, even Boris's friends called him "selfish, lazy and arrogant". They recall his tenuous grasp of the facts. They claim that he regards not behaving like a total scumbag as hopelessly bourgeois and gauche. What a guy to represent our capital city.

It is too late to elect anyone else as Mayor. It's too late for the Belgravia cuckold and the mop-haired child. It's too late for David Cameron (ha ha) to distance himself from his bad choice of chum. But if we don't wise up in 2012, the people of London are as dumb as all the women who fall for Boris's selfish charm. And I for one don't want another dose of his je ne sais quoi.