Come back Roy Chubby Brown, all is forgiven! And how about a public apology to Bernard Manning while we're at it? Why? Because the dreaded mother-in-law figure that they spoke of so caustically is alive and kicking – but unlike those comedians' crude caricatures, this time it's the daughter-in-law's mother-in-law who's doing the kicking. She is one Carolyn Bourne, 50, whose admonishments to her son's prospective bride, 29-year-old Heidi Withers, raised not only eyebrows but also questions about etiquette in the internet age.

"When you are a guest in another's house, you do not declare what you will and will not eat," Mrs Bourne wrote to Ms Withers in an email that was soon winging its way around the world. "You do not take additional helpings without being invited to by your host [and] ... you do not lie in bed until late morning in households that rise early – you fall in line with house norms."

"You should never, ever insult the family you are about to join at any time and most definitely not in public," Mrs Bourne continued. "I gather you passed this off as a joke, but the reaction in the pub was one of shock, not laughter."

These diktats are, for the most part, utterly fair enough. You don't drag up the little rascal – funny smells, smart-arse remarks and all – only for him to disappear into the sunset with someone who makes you want to eat glass.

Tensions between mums and their son's partners run high on both sides of the relationship. It's a tricky bond to negotiate, because each party judges the other on the same standards – that is, on simply being a woman. And, by default, the criteria that both are being marked on vary wildly, given generational divides and more immanent concerns. Your mother-in-law might take a dim view of your tattoo, for instance, but she hasn't taken into account the number of celebrities you've met and how good your manicure is.

But that's not to say that Mrs Bourne should have put the lot in an email and fired it off. That the entire diatribe has now become a public spectacle is, possibly, no less than both of them deserve. Dressing-downs, domestic ones particularly, are supposed to occur face-to-burning-face and behind closed doors, so that they can be forgotten about as quickly as possible in the name of bonhomie and a Sunday roast that doesn't turn to ash in the mouth.

It's a terrible catch-22 of falling in love with a Nice Boy: he's usually nice because he's been brought up well – but if he's been brought up well, his mother probably dotes on him. And that's when she starts emailing you about your slovenly habits. A friend told me about the time she and her fiancé announced their engagement and his mother wailed, "You're taking my son away from me!" (They divorced a few years later, and my friend resisted the temptation to say "Here you go – have him back!")

"Unfortunately for Freddie, he has fallen in love with you," Mrs Bourne added in her e-tirade. "If you want to be accepted by the wider Bourne family, I suggest you take some guidance from experts with utmost haste. There are plenty of finishing schools around."

This, quite clearly, is the stuff of nightmares – in a fluid society where eligible young men aren't simply packaged off at birth to the pallid daughter of the neighbouring estate, mothers-in-law have lost some of their dominion. And for any woman entering the household of an older, wiser, redoubtable matriarch, pitfalls abound.

Meanwhile, the pleasure of going home to one's own parents is the fact that they dote on you and you don't have to lift a finger; when visiting the in-laws, this should be applied inversely: do everything, eat everything (but don't ask for more), and be generally helpful, but not obsequious. Suppress all natural reactions to the point where even your boyfriend wonders who on earth he has brought home with him. And don't mention money – or if you do, gauge your in-laws' attitude to it first. Do not, as Ms Withers did, assume that they have similar tastes to you.

"You regularly draw attention to yourself," Carolyn Bourne continues. "Perhaps you should ask yourself why. No one gets married in a castle unless they own it. It is brash, celebrity-style behaviour."

Four easy tips that would have helped Heidi out: it's the "sitting room" not "the lounge"; taking your shoes off as soon as you get through the door is common; always leave your knife and fork at quarter to four on your plate; and don't be fussy, obnoxious or lazy. Simple enough, really.

But does the "monster-in-law" of popular myth – the jealous, protective, imperious Gorgon at the head of the table – actually exist? Well, not really. It's much more a misogynistic construct built around the fact that women, supposedly, find it terribly hard to get on with other women. In fact, the likelihood is that a mother-in-law will welcome her son's girlfriend with open arms (anything less, by way of reverse psychology, will drive him further into the arms of the vacuous young flibbertigibbet) and befriend her (all the better to gang up on him about cutting his hair or doing the washing up).

From the nervous first meeting and that ingrained urge to impress, to the birth of one's first child and the elaborate paraphrasing of "shove your advice where the sun don't shine" into something more delicate, mothers- and daughters-in-law are bound to rub each other up the wrong way at times. It happens in any close relationship – it's just that you can tell your mother/sister/best friend to bog off and they won't be offended.

And Mrs Bourne's email – while flagging up the importance of manners more generally – certainly contravenes what most people would think of as a dignified response; we're far more likely to put up and shut up in the face of anti-social behaviour, which is why the outspoken doyenne has garnered so much support for her actions. There is clearly a fervent but subliminal feeling out there that yobs too often get away with their antics, without being told what's what.

But the Venn diagram of legend – warring women either side of a baffled young man – is a cartoon that simply doesn't exist in households that get on with each other. I just hope my future mother-in-law, whoever she may be, isn't reading this column. And if she is, she hopefully won't understand email.

h.walker@independent.co.uk