Back in 2008, Oprah Winfrey dedicated an entire episode of her show to making over a hapless group of women she dubbed "schlumpadinkas". For the uninitiated (and the word is one Winfrey invented herself), a schlumpadinka "dresses like she has completely given up - and it shows".
The episode featured women guilty of "non-stop frump" - wearing nothing but baggy T-shirts and elasticated waistbands - on whom Winfrey bestowed smart new wardrobes to transform them from "schlumpy to sexy".
We all know the type. Many of us have indulged in a little schlumping ourselves. You may even be a fully-fledged schlumper who sees nothing wrong with wearing tracksuit bottoms in the car or pyjamas at the supermarket. There's nothing to be ashamed of: dressing casually is comfortable, easy and requires very little thought. There's no laying out of the outfit the night before; no worrying that your Zara bomber jacket is last season's - simply fish out those sweatpants, pop on some trainers and a velour top, and off you go.
Indeed, though Winfrey invented her word six years ago, schlumpadinkas are a breed on the rise in Britain. It can be no coincidence that the past few years have seen a boom in popularity of tracksuit bottoms (an ode to which featured in a recent edition of Vogue magazine), hoodies (now sold by Zara Phillips in her range of equestrian clothing) and scrunchies (sported by the likes of Madonna, Angelina Jolie and even Hillary Clinton). Dressing down has become the new dressing up, with celebrities sporting gym wear and festival scruff everywhere from black-tie dinners to upmarket shops and red carpet events.
At last, however, this strange phenomenon has an explanation. A study by researchers at Harvard Business School has revealed that dressing down can lend people an air of "competency" and boost the wearer's status in the eyes of those around them. Wearing gym gear in a fancy clothes shop, for example, can create a sense that the person is more of a "big shot" than someone dressed in luxury items, because that person has deliberately flouted the traditional dress code.
"If you're willing to deviate, there are upsides," said Silvia Bellezza, one of the three authors of the study published in the Journal of Consumer Research. "In other words, when [dressing down] looks deliberate, a person can appear to have a higher status." So, shop assistants in an expensive store in Milan assumed that test subjects wearing casual clothes were more likely to be wealthy and sufficiently confident in their social status not to need to dress up (think Sam Cam and Prince Harry's laidback cool). Similarly, an unshaven professor was accorded more respect than a clean-shaven academic.
Those who live off their looks have known the power of this for years. "In Hollywood it's a given that you dress down most of the time - look how many times Britney Spears and Gwyneth Paltrow get pictured in their sweats," says Nick Ede, a brand commentator. "Then on the red carpet there's a transformation that gets the world's press buzzing. This style law has now filtered through to the masses: it's not right to be slick and groomed all the time."
So, if you want to get ahead, ditch that Chanel trouser suit for jeans and a hoodie - looking like you've just woken up might just help you rise in the world. When in doubt, turn to those already pulling off schlumpadinka chic to perfection...
The Gym Bunnies
Strictly Come Dancing champion Abbey Clancy is the covergirl for this look, frequently photographed wearing black leggings, tracksuit bottoms and zip-up tops. To her credit, she is often on her way to - or from - the gym, but, far from being effortless, Clancy's style is a carefully crafted affair. Her abs are perfectly honed, her gym bag is from Givenchy and her leopard-print trainers are Stella McCartney (who famously featured sportswear with high heels in her spring/summer 2014 collection).
Pop star and newly returned X Factor judge Cheryl Cole is another fan of work-out chic. In a video for her song Ghetto Baby, she sported three-stripe Adidas tracksuit bottoms; an Eighties-throwback look also favoured by the singers Rihanna and Elton John and the actress Anne Hathaway.
Cole's dressed-down style may look a bit lazy, but it's borrowed directly from many a catwalk show: Isabel Marant designed a grey tracksuit for H & M; Christopher Kane's jogging bottoms sell for £75 at Topshop; and Balenciaga's leather-panelled hoodie is a staple of the rapper Kanye West.
The Make-Up Free Models
Model Cara Delevingne rocking her signature 'grungy and dishevelled' look. Photo / Getty Images
Cara Delevingne leads the pack of fashionistas who take the pared-down, couldn't-care-less look to the extreme. Despite being the world's highest-paid model, earning an estimated $46 million (£28 million) in the past year alone, the 21-year-old's style can only be described as a mess. Beanie hats, ripped jeans, moth-eaten T-shirts, Converse trainers, even the occasional onesie - Delevingne seems to pride herself on looking grungy and dishevelled.
Don't be fooled, though - her intention is anything but: tomboy styles dominated at last month's London Fashion Week and Delevingne was centre stage. "I love comfort," she once said in an interview, "because I spend most of my time in very uncomfortable things, so it's all about trainers and flats." In other words: you know I look good when I'm on the catwalk, so why do I need to prove myself when I'm not? Many of Delevingne's friends also prefer casual chic: singer Rita Ora (a fan of neoprene sweatshirts and tie-dye trousers) and presenter Alexa Chung, whose tousled hair and slept-in make-up have become her trademark.
The Scowling Starlets
Twilight starlet Kristen Stewart is often seen on red carpets in a dressed-down look. Photo / Getty Images
While most A-listers spend tens of thousands on their red-carpet appearance, there are some who roll up looking like they've just rolled out of bed. Step forward Kristen Stewart, Twilight star and one-time girlfriend of the actor Robert Pattinson, whose dressed-down look - baseball caps, Timberland boots, frizzy hair and a scowl - has earned her many a spot in magazines' "worst dressed" lists. It's not that Stewart doesn't care, however; her anti-establishment scruffiness fits perfectly with her rebellious attitude. To dress any smarter would simply ruin her image.
She's joined by British singer Adele, who, though a head-turning glamazon on stage, prefers to don oversized cardigans, baggy T-shirts and shapeless leggings at lower-key public events. And of course, who could forget Billie Piper, the singer-turned-actress, who has refused to shun her signature bedraggled style on outings to the Groucho Club and Glorious Goodwood. Both, it must be said, are busy working mums - but most busy working mums aren't being chased by the paparazzi everywhere they go. The unwashed, unbrushed look is a very deliberate choice.
The Scruffy Billionaires
Mark Zuckerberg. Photo / AP
It's not just well-known women who are opting to dress down. Mark Zuckerberg, the founder of Facebook, has been criticised for attending business meetings and presentations in a hoodie and Adidas slip-on sandals. Sergey Brin, the co-founder of Google, wears similarly casual shoes, while Steve Jobs, the late CEO of Apple, was rarely seen without his uniform of jeans, black polo neck and New Balance trainers. If you're a Silicon Valley billionaire, it appears, you can wear what you want, where you want. With that much money in your pocket, nobody's going to tell you otherwise.
Over here, too, the trend is slowly taking off outside of the billionaire bubble - as modelled by Russell Brand (a fan of week-old T-shirts and scuffed boots) and Jude Law (baggy shorts and baseball caps). When Soho House, the private London club, introduced a "no suits" rule in 2011, it faced a backlash from City members who claimed its anti-tie rule was "dated". Sister club Shoreditch House, however, retains its dressed-down rule, and today welcomes suitably fashionable tracksuits, hoodies and trainers through its doors.
Britain's ever-growing band of schlumpadinkos will be delighted.