Cameron Diaz is good at a lot of things: surfing, picking handsome and famous boyfriends, remaining semi-normal despite being beautiful and rich. What you didn’t know was that she’s also really great at designing handbags.

That’s what’s on her CV, at least, given her new role as artistic director at Pour La Victoire, announced today on Women’s Wear Daily.

Cameron Diaz is not the first celebrity to be given a job to which she is wildly unsuited, and she won’t be the last. From Lindsay Lohan to Lily Allen, the roll call of names who have become more than just famous faces in fashion is as long as it is uninspiring and vaguely depressing.

What are their credentials, after all? Why should these people, styled and (in many cases) manufactured to within an inch of their lives, have any bearing on what we ourselves choose to look like? Every so often, the wheel of fame and fortune throws up someone genuinely charismatic; these are, on the whole, not the people who start their own clothing lines.

Kate Moss’s collections for Topshop truly epitomised celebrity fashion: a range based on pieces we had already seen the model wearing (and werking) from her extant wardrobe, rather anything that tried to be her own aesthetic vision.

It offered us the chance to look like her, which – at the time – fitted the fashionable zeitgeist perfectly.

But for Paris Hilton to put her name to a totally nondescript halter-top or pair of glittery heels is rather different: the pieces celebs end up ‘designing’ are, for the most part, things you can’t see them ever wanting to touch with a barge-pole, let alone wear in public.

[I remove from that bracket Lindsay Lohan, who without doubt would have had a night out in the sprayed-on jeans, bandeau tops and nipple pasties she disastrously created for the Parisian house of Ungaro in 2009. But you’d be hard pressed to find anyone else who would have worn it.]

There’s no doubt that the right celebrity in the right campaign can persuade you to part with your cash – that’s precisely how their good looks and influential cachet works. But when that same person purports to be involved in the creative process, doesn’t all this feel even more farcical than the notion of buying something because a famous person likes it? Don't you just want to say 'oh as IF you designed it, Cameron, in between having a kale shake and being on a sun-lounger all day' ?

We’re just showing ourselves up by falling for it – and the whole cynical process will remain viable and credible until the scales fall from our eyes.

In this age of internet fame and fandom, designers have become celebrities in their own right. We don’t need actors or It-girls to tell us what to wear. What feels so retrograde about it is the fact that the most stylish consumers rarely look to the red carpet or to A-listers for their fashion hits any more: inspiration comes from street style pictures, from real women around the world (like our Global Stylers) wearing what they like and wearing it well.

So stop, celebs. And stick to what you’re good at instead – like surfing, and picking handsome and famous boyfriends.