“Are you on Facebook?” is all I have heard for the past few months, and now the question is beginning to sound as if not being on Facebook is the same as sharing Jim Davidson’s world-view. I admit to being gobsmacked, in the same way that I despair when I see a thirtysomething reading Harry Potter, or a grown woman wearing plaits. One minute, Facebook is the one that isn’t MSN that is keeping kids glued to their computer screens; the next, it is the only way for switched-on grown-ups to stay in touch. Leaving aside the obvious thought (dear God, is there nothing that exists exclusively for the young?), this latest development says something tragic about modern-day adult friendships. Well, two things actually: that we are obsessed with quantity, not quality; and that we feel no shame in collecting friends like trophies. That’s handbags, surely.

If you are on Facebook, presumably you tell yourself that, in an age when people frequently move around and switch partners, it provides a valuable means of keeping in touch. But, really, Facebook is just a big fat excuse for making yourself feel good by association with lots of random people. This is a perfectly reasonable ambition if you are desperate to drum up enough bodies to have a party in the kitchen (and you are 16), but for real grown-ups it is not just sad; it’s really sad. And that’s before the word “friendship” has entered into the equation. Facebook is to friendship what Ziggy and Chanelle (below left) are to enduring love. It is an exercise in narcissism, pure and simple, providing the feelgood factor of being liked by many without having to get off the sofa, let alone get to know any of them.

Wouldn’t it be more accurate to say that Facebook “friends” are, in fact, “people I have met”, including the boys who used to work in IT, your diving instructor, the bloke who gave you his card after the wine tasting – people whose houses you have never been inside, whose characters you couldn’t vouch for in a court of law. Judging by the e-mails I’ve had from people who have added me as a friend on Facebook, you don’t have to have had any social interaction whatsoever to qualify.

In reality, we have no more than eight people in our lives who we can call “real friends” (go on, count them), and if you’re a man, make that one. In case a reminder is necessary, a friend is someone who has held your head over the loo; who has sat up until dawn with you raging about the vileness of men; who knows all your secrets; and who has known you for longer than your present incarnation, and preferably through all of them.

Under 21 is when you collect people, any people, in case they know other, better people or are having a party – and that is the right time for Facebook. So leave it to them. There’s always Friends Reunited if you’re desperate.

Times recommends

• How I lost the gift of joy for a while
• How to get Coleen Rooney's post-baby body
• The A-Z of winter style rules