"Small," reads the label dangling from the first tank top on the rack at the Brandy Melville store in SoHo. So does the one behind it. And the third, fourth, fifth -- they're all small. In fact, nearly every single piece of clothing in the store is either labeled "small" or "one-size."

Welcome to the hottest teen clothing retailer in the U.S., where the garments are designed for just one body type: thin. Brandy Melville has stormed onto the teen fashion scene with its "one-size-fits-most" policy and whimsical California vibe. Despite its modest fleet of 18 stores in the U.S., mostly in California and around New York City, it's one of the brands with the fastest-growing popularity among American teen girls, according to a semiannual survey from research firm Piper Jaffray.

Who is the Brandy Melville girl? One look at the brand's website and Instagram account reveals her: young, white, skinny and long-legged.

"It's an exclusivity thing: Congratulations, you fit in the clothes! Join the club," said Justina Sharp, a 17-year-old fashion blogger who runs her style site, A Bent Piece of Wire. "There will always be the girls who will try to squeeze into it. They'll do whatever they can to fit in Brandy Melville."

While teens fawn over the retailer's assortment of crop tops, halters, cardigans and more, critics say Brandy Melville has raised the stakes when it comes to fat-shaming. Though the fashion world has long fetishized skinniness, and some labels cater to even slimmer profiles, few have taken size exclusivity this far. Yoga-wear company Lululemon, which admits plus-size customers aren't part of its strategy, does offer sizes from 0 to 12. Even Abercrombie & Fitch, derided for ignoring overweight kids, sells clothes with extra-large on the labels, up to size 14.

At Brandy Melville, nearly all the clothes are small, though a medium will pop up here and there. To be able to shimmy into Brandy Melville's only size of skinny jeans, a girl would need to have a 25-inch waist -- that's around a size 0 or 2, depending on the brand. Most skirts and shorts on the website are about the same size. Similar skinny jeans at teen fashion powerhouse Forever 21 span sizes from 24 to 30 inches. In the U.S., the average 16-year-old girl is approximately 5 feet 3inches tall, weighs about 138 pounds and has around a 31-inch waist, according to a 2012 report from the Centers for Disease Control and Prevention.

Rachel Simmons, co-founder of the Girls Leadership Institute, a national nonprofit group, said Brandy Melville puts teen girls through the "paces of the popularity jungle," recreating the challenge of having to be the best and coolest in school.