How much, on a scale of one to ten, do you care that supermarkets are losing £200 million a year to “grazers” - people who shop while stuffing their faces with food for which they have no intention of paying? I'm guessing that, essentially, you don't give a toss. The Big Four make umpteen billion pounds out of us every year, you think, they can cope with losing the odd, sweaty Scotch egg!

Well - and this amazes even me - I care. It's not that I'm sucking up to supermarket bosses because I might one day need a shelf-stacking job (well, maybe a bit - these are uncertain times), or even that I object to such shoppers euphemistically being termed “grazers” when they are just grubbing shoplifters. No, it's that I know how pig-ignorant supermarket customers can be and I'd like to see them punished - preferably with an electric prod.

As I've mentioned before, I was a trainee manager for a supermarket for eight of the most miserable months of my life (on second thoughts, shove that shelf-stacking job) and have seen the transformation that takes place whenever people get behind a trolley. They go into a wild-eyed trance, apparently convinced that they're the most stressed and busy people in the world, tutting and sighing and stampeding the aisles in very bad moods. But in those days I had to be diplomatic about their beastliness, and now I don't.

I recall having to remain polite while being: bawled out by a businessman for refusing to reduce a packet of best steak that I had watched him deliberately damage with his thumb; summoned by an outraged woman and ordered to place loose new potatoes in a plastic bag for her because they were “covered in soil” (new potatoes - ya don't say?); called a “snotty cow” for merely pointing out that a customer's money-off vouchers were for a different supermarket chain. I have witnessed an actual fight between two women over a tub of coleslaw reduced by 30p, and on the checkouts had to whistle while yet another person screeched “Don't pack the eggs at the bottom!” as if I was a drooling halfwit.

This week a spokesman for GS4, a supermarket security firm, said of the grazers: “We find baskets littered with empty wrappers and half-eaten bunches of grapes. This is theft.” Yes it is - and so, by the way, is standing there reading all the newspapers, then walking away without buying one. Journalists have mortgages too, you know: how would you like it if I came to your kitchen showroom and legged it with a pair of taps?

But those months in hellish acrylic made me realise that some people regard big supermarkets much as they regard the stationery cupboard at work. It's not really stealing because they owe you, eh? That's probably why the equivalent of two million people admit to nicking stuff when using the self-scan checkouts. Well, it's a drop in the ocean, a victimless crime!

No it isn't. Many small suppliers are paid by volume sold in store, not delivered, so you may as well break into their houses and nick their DVD players. And when you've guzzled down your stolen tuna sandwich and shoved the rancid packaging behind the sanitary towels (nice touch), who do you think has to fish it out and probably get a rollicking for not being vigilant enough? Well, it isn't Lord Sainsbury.

So I feel only comradeship with the Tesco employees who have gone online to say what they cannot say to many of their customers' faces. Hats off to the worker voicing her umbrage at customers who put their money on the conveyor belt rather than in her hand, which I remember left me feeling like John Merrick with added leprosy. “Do we have some kind of infection that you might catch? Ignorant b*****ds,” she says. Full sympathy to the one who is driven mad by the frequently asked question: “Excuse me, do you work here?” and who longs to reply something like: “No, sir, I just wear this Tesco uniform because it's bang on trend!”

I'm not saying that all shop staff are saints. How could I when behind the tills at the Disney Store stand the grinning embodiments of human insincerity. After they have perfunctorily patronised your child with feigned interest in her Princess preferences, it's back to the steely hard sell. “Would you like me to pop this in a gift box for only £2 todaaay/ buy a re-useable carrier bag for only £2 todaaaay/ purchase this pointless cuddly toy at the special discounted price of only £15 todaay?” It makes me nostalgic for the seasoned churlishness of the lads in one of our local convenience stores where some clientele are so light-fingered the tinned salmon has to be kept behind the grille next to the Lambert & Butler.

What I am saying is that supermarket workers put up with a lot and so it's obvious why Anna Sams's new book, Les Tribulations D'une Caissière, in which she dishes the dirt on customers' rudeness, has become an international bestseller. The book, soon to be released in Britain, must feel like a sweet caress to millions of employees who are insulted by the hour. Sams, a college graduate in France, ended up working for eight years as a “beepeuse” on a supermarket till and was frequently left aghast by the public's automatic assumption that she was not only an invisible idiot, but a deaf one. Once, standing at her till, a woman chastened her testy child by saying: “You see, dear, if you do not work hard at school, you will become a cashier, like the lady.”

This is why checkout staff love to tell the joke about the surly customer who walks into a supermarket and throws one bar of soap, one toothbrush, a pint of milk and a TV dinner for one on the conveyor belt. “Single, are you?” asks the cashier. “How did you guess?” asks the customer, sarkily. The cashier smiles and replies: “Because you're ugly.”

Yes, let's learn a lesson from Anna Sams and the Tesco Facebook gang: workers have feelings too. And there are myriad ways of taking revenge - even for a “loser” in a nylon tabard...

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