You know something's gone really big when a politician starts talking about it to gain cred. In Britain, London Mayor Boris Johnson has boasted about his Union Jack onesie; deputy Prime Minister Nick Clegg has claimed to own one; and, in January, Prime Minister David Cameron said he was jealous of his kids' all-in-ones.
Yet the idea that has sparked a thousand pictures in trashy magazines is 100 per cent Norwegian - and the people behind it say bring on the publicity. "Since we started it's always got attention," says Thomas Adams (27), who co-founded OnePiece in 2007 with pals Henrik Børke Nørstrud (30) and Knut Gresvig (31).
"Norwegian politicians have them too, and it's all good news for us."
The three friends had the idea on a cold Sunday in Oslo, when Børke Nørstrud's hoodie kept riding up. The trio, who ran an online clothing store at the time, decided to sew his pants and hoodie together - and the rest is history. From the initial 100 they made in 2009, Adams now says they've sold "hundreds of thousands" of the orginal OnePiece, even in the face of many imitators (that's you, Primark).
"The success has been extraordinary - it's been an amazing journey," says Adams.
Charting An Unlikely Fashion Phenomenon
Thomas Adams rocks up in Oslo wearing a purple onesie.
His friends are incredulous, but want one.
Peaches Geldof and Davina McCall are spotted in them, then actress and trendsetter Sadie Frost says she's going to buy onesies as Christmas presents for all her friends.
Boy band One Direction regularly wear OnePiece onesies on the way to coming third in UK talent show The X Factor.
After calling the USA "evil" for its healthcare system, Canadian teen star Justin Bieber makes amends with a stars and stripes OnePiece.
Swedish pop starlet Robyn is spotted in a OnePiece during a pre-gig soundcheck.
Footballer Mario Balotelli poses in a camouflaged OnePiece next to his camouflaged Bentley.
Brad Pitt is spotted in a rather cheap-looking, black onesie (not a OnePiece).
Singer Cheryl Cole wears one to the top of the Eiffel Tower. Sacré bleu!
In 2012, London Mayor Boris Johnson and the UK deputy prime minister said they owned onesies. Now British PM David Cameron claims he's jealous of his children's onesies.