Anna Sam has witnessed thieves, drunks and lovers. She has put up with rudeness, indifference and ignorance, and has gleaned what she describes as an almost unparalleled insight into the full extent of human stupidity.

Now, after eight years as a supermarket checkout worker, she has turned the table on her customers with a book that depicts their behaviour as they push their trolleys around the aisles.

It is not a pleasant sight. She says that social etiquette is cast aside as shoppers jump queues, squabble and show the utmost disdain for the women, and occasionally the men, behind the till. “You see people as they really are,” Mrs Sam told The Times. “They behave as though they were in their living room and they forget that the checkout girls are watching them. It's incredible.”

Often appalled and sometimes amused at the antics of the average French shopper, Mrs Sam, 28, began to write about her experiences in a blog last year. This proved a success - with 600,000 visits to date - and thrust her into the media spotlight as the public voice of the supermarket worker in France. After she appeared on prime-time television, publishers fought with each other to offer a book deal to the woman described by one daily as France's most popular check-out employee.

The work, Les tribulations d'une caissière (The Trials and Tribulations of a Check-Out Girl), was published last week amid another swirl of publicity. But Mrs Sam never intended to end up in a supermarket. She was a literary student in Rennes, where she specialised in Jean Ray, a cult Belgian author dubbed the Edgar Allan Poe of the French language.

Like thousands of French university graduates, Mrs Same failed to find a job to match her qualification and so went to work in Leclerc hypermarket in Rennes, where she earned €8,160 (£6,520) a year for a 24-hour week.

“There are a lot of students with literary, sociology or artistic degrees in supermarkets in France,” she said. “Not many of them really want to become checkout workers.” For hours on end - a typical shift goes from 9am to 2pm or from 3pm to 8.45pm - they scan goods, announce the total bill and take the money. “And all with the most sincere of smiles.” On average, they say bonjour and au revoir, bonne journée 250 times a day; merci 500 times a day and les toilettes sont par là 30 times a day, Mrs Sam said.

But there is precious little return for these efforts. Many customers treat la caissière as though she was not there, staring past her and failing to say hello back, according to Mrs Sam. When they do speak, it is often with condescension or anger. “It's not a majority who are impolite but it's not far off,” Mrs Sam said. “They are often very vulgar. They are fed up with being there and they take it out on us.” Insults fly as staff refuse people with 11 items at the ten-items-or-less checkout.

Then there are the mothers who point at the checkout worker and say to their child: “You see, darling, if you don't work hard at school, you'll become a caissière like the lady.” Mrs Sam tells them that she had five years of university education.

But Mrs Sam's most surprising claim is that supermarkets are “a lot more erotic that you would think. “You would be surprised at the number of kisses in the aisles ... at hands on bottoms in front of the frozen goods, at breasts caressed in the woman's lingerie.”

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