The story of the Topshop mannequin is a body image one, sure: mainly that. But it carries some social media messages, too: viz, that if you want to have a Facebook page, and invite your shoppers to “engage” with you there, then sometimes they may say things that don’t suit you at all. So it was on Monday, when Laura Berry took a picture of a mannequin in the Cribbs Causeway store outside Bristol: she put it on their Facebook page, with the message: “I’m calling you out, on your lack of concern for a generation of extremely body-conscious youth.”

The store, after trying and failing to contact Berry privately, was reduced to a public justification. “As the mannequins are solid fibreglass, their form needs to be of certain dimensions to allow clothing to be put on and removed easily; this is therefore not meant to be a representation of the average female body.” Huh. Things that are fibreglass need to be really, really small. Who knew?

The mall in Cribbs Causeway is everything you’d want from a mall, if that’s what you’re into: shops, more shops, further shops and the piped smell of pretzels. Their Topshop is particularly good, apparently: Jordanne Hooper said that the new stock arrives in the store within a day or two of featuring in magazines. This is the litmus test of shopping excellence; in Bath, you could wait a month. I met Katie Toogood, 20, and her mother, Jayne Toogood, 49, in the mouth of the store. The offending mannequin – dressed in skinny jeans to maximum skinny effect – may have been removed, but obviously they’re all the same size, so there is no shortage of sculptures with unnaturally skinny legs and fingerless hands like mittens.

Katie lost her entire teenage decade to anorexia and was in a psychiatric unit for 10 months when she was 15. Jayne gestured to one of the mannequins and said: “That’s what Katie’s legs looked like when she was in hospital.” Her daughter said: “I think people miss a massive part of what eating disorders actually are. For me, it was stress-related, and not about body image. My mum got cancer and I was struggling to cope and get straight As. Something had to give. But it doesn’t help when you’re being told that you’re too underweight to be released from hospital, and then, when you come out, the mannequins and models are thinner than you are.”

Frankie, 19, is a massage therapist, and says something similar: that to relate it to eating disorders is melodramatic and not really necessary. “It’s definitely about making us all feel a bit more shitty about ourselves. I’ve just come back from holiday. Before I left, I was thinking: ‘Oh my God, I’m too big for a bikini.’ But then you get there, and people are all shapes and sizes.” She adds, though – and maybe I detected a trace of mischief, or maybe I just expect puckishness from people called Frankie – “in the nicest way possible, I don’t think mannequins should be too big, either. Nobody would like that. They’d say it was encouraging obesity.”

Jill and Roma, both 59, find it bizarre that skinniness has become this prized quality. “I’ve got two girls,” said Jill, “in their 30s now, but I think this is a bad influence. It makes them think they have to be skinny lizzies. My daughter was actually classed as anorexic at one point, but she wasn’t. She was just very thin because she went swimming a lot.” “The thing is,” Roma adds, bewildered, “is thinking it’s something to aspire to.When we were young, we had normal, basic food. And everybody looked the same. You didn’t have these huge, fat people.”

It’s fascinating how many people make that segue: one minute they’re talking about thinness as a peculiar thing to idealise, and the next they’re slating fat people. “Everyone wants to change something about themselves, anyway,” said James Hunter, 20, who works in a shoe shop. “People are really conscious about having wide-set feet,” agreed Jordanne, who works with him. “And if it’s a pointy shoe and you suggest they go up a size, they hate that. Nobody wants to go up a size.” She says the clothes shops are missing a trick, because clothes look nicer on people with curves and they would sell more if they acknowledged that. “Primark mannequins are a bit bigger, but it’s still pretty risible.”

It is quite bizarre, the desire always to be smaller, a motivation separate to aesthetics or sex, an act of self-erasure. Though that doesn’t make it a picnic being a boy. James pointed out: “I have to wear women’s jeans all the time because I’m so short.” “So do you feel like you’re under pressure to be taller?” I asked him. “Not really,” he explained very slowly. “Because I know I’m short.”