Harriet Walker: Karl Lagerfeld's Kash-and-Karry at Chanel's Paris show brought out the worst in fashion magpies

The world is full of contradictions: jolie laide, the sublime and the ridiculous, Tony Blair. But last week I witnessed one of the most staggering. A contrast of primordial proportions. As if you had stood Bill Gates next to a monkey: you could see the similarities, the shared root; but beyond hairline, there was little in common.

It was at the Chanel show in Paris, a celebration of consumerism breathtaking in its scale, laid on by the brand that sits atop the societal pyramid of fashionable aspiration. It's les noix de chien of fashion, if you will.

Designer Karl Lagerfeld chose as his setting a supermarket. But he didn't just close down his local branch of Spar and ask models to trot up and down the aisles. He installed an entire own-brand emporium inside the City of Light's Grand Palais, containing everything from fruit to feather dusters, tisanes to toilet brushes. It was a comment on consumerism; it was the apex of consumerism; it was the cordon bleu of eating oneself. It was astonishing, and beautiful, and breathtakingly ballsy and excessive. It was fabulous.

And so were the clothes on the models, who picked up and put down produce as convincingly as we all do among the shelves, trotting between fruit and cake and back again, debating between the cheap mustard or the one with the nice packaging. Except there was no such dilemma in Karl's Kash-and-Karry, because all of the packets were fancy – they referenced Chanel in "Coco" Pops, in quilted coffee-filter papers that were a nod to quilted handbags, even in chainsaws that spoofed their golden trim.

Understandably, they caught the eye of the fashion magpies in the audience. And so, as soon as the show was over, they leapt from their seats, hurled themselves down the catwalk and stampeded towards the shelves. Top targets in the smash-and-grab that ensued were the "Mademoiselle Privé" doormats, the appliqué camellia washing-up gloves, and the logo-embroidered hi-vis jackets (perfect for cycling, ma cherie).

I hung back, slightly aghast. We had shifted so quickly from what was a stately, elegant display to the playing out of the most vile sort of psychology, comic in its inelegance but depressing in its indignity. People were sprinting, shoving, practically maiming to get the stuff – and in doing so, they pulled it apart.

Standing in the middle of it all, my fingers twitching to grab something too, I felt the serene realisation washing over me that this was humanity at its most base, and most urgent. That when electricity and water and law enforcement fail and the end comes, this is how it will happen for our children's children's children. We will trip up our own kind for resources; elbow each other in the face for vittles; we will trample on our dignity and our companions alike to make sure it is our grubby little fist that clamps on to the valuables, not theirs.

I picked up a biscuit tin from the nearest shelf, conflicted. If everyone at the show was to have a souvenir, then I might as well too. And at least I hadn't broken a sweat or anyone else's limbs to get it, I reasoned with myself, as people ran to and fro around me with trolleys piled high and plastic buckets full of the world's most haute comestibles.

As an anxious and awkward person, the idea that other people – my peers, my colleagues, my role models within the industry – might see me snuffling at the wares, knocking down shelves and stamping on weaklings, was akin to them seeing me naked. It would keep me awake for years.

So I put the biscuit tin down before I reached the exit. And during that long walk to the door, I saw a security guard cowering under the hordes who wanted a ketchup bottle, batting people away with his right hand as several more rushed his left side; I saw another running after a woman clutching a stack of boxes and tins (all empty, I'll add, for display only), who was eluding him as quickly as he could give chase. For at the door, those in charge were confiscating the goods hauled and patting down people who'd stashed them under their coats. We'd debased ourselves for nothing – it was the fresh fruit and vegetables that we could take, not the logo'd products.

Chanel later announced that the fresh produce from the show would be going to a homeless charity. Perhaps the tarnished must-haves have gone into an archive. Whatever; at least they'd been taken away from us.