It takes a brave client to go with a spot conceived around the waking nightmare of its target audience, but the risky strategy seems to have worked for coffee giant Folgers as its newest spot has become something of an Internet phenomenon.

Harnessing the power of irritation, "Happy Mornings" (Saatchi & Saatchi, NY) aims to take the brand to a younger, hipper consumer by bringing all the dreaded aspects of 'morning-ness' to life, suggesting coffee as the antidote.

The theme's messengers are the creepy brain-children of Saatchi creatives, Leo Premutico and Jan Jacobs. As the sun rises from a tranquil ocean, an ominous "Ha cha cha cha" kicks in and a mass of scary, shiny and very blonde yellow people spill out of the sea and across the town like a slick of golden syrup.

They swing their way into those intimate waking moments when you just want to be left alone to get to grips with the start of a new day. No place is sacred. In a relentless tide of crazed optimism, they power-walk and dance through the streets, breathing clouds of butterflies and invading bedrooms and bathrooms, grinning down from ceilings and out of mirrors.

Premutico and Jacobs say the yellow people represent what it's like to be woken up by daylight when you're a 20-something university student, pitched into the daily ritual of professional work.

"We had a classic problem," says Jacobs. "Making sure the spot is just irritating enough, striking the balance between being annoying and entertaining." And no doubt, whether that balance was met will be debatable by some.

Everything - the looks and clothes of the yellow people, their moves and their song - had to be just off-centre enough to unnerve and intrigue the audience, but also make them laugh with recognition. "Hasn't everyone been in that situation in the shower where you just want the light to stop?" asks Jacobs.

The spot was shot across five days in New Zealand: three were spent filming live action and the remaining two with the yellow people writhing and gurning against a blue screen, followed by an intense fortnight in post-production.

"The location decision was financial to a degree," says Premutico. "Because the spot was going viral and we weren't sure what the impact would be, it made sense to go down there and do a complete talent buyout, take advantage of that quirkiness, and work with a director [The Sweet Shop's Steve Ayson] who we knew could nail that kind of humor."

Serendipity came to their aid in the form of choreographer Michael Rooney, who happened to be shooting in the southern hemisphere at the same time. Charged with generating an anti-Broadway awkwardness that celebrated the embarrassing side of happiness in just three days, Rooney came up with sequences that gave the yellow people full expression, so much so that they'd go off to the side and invent their own gyrations, many of which were adapted by Ayson and his team.

The music was created by the established LA composer and lyricist Alan Zachary and Michael Weiner, who also had to write a song that straddled the thin divide between being irritating and sing-along happy, keeping it memorable whilst matching the creepiness of the characters. They delivered, says Ayson.

"Everything was storyboarded, apart from a shot where we had three yellow people floating through the sky," he says. "And we had to play the track on every single take. To begin with, you could see the crew wondering what they'd got coming. Then you'd see these hardened, tattooed old grips with their feet tapping away on the dolly. It poisoned us all."

Ayson says it was tough getting used to just missing the mark, deliberately, on all fronts.

"We'd planned and approached it with that idea all along, but several times I had to remind myself that we were going for that sense of creepy imperfection," he adds. They had to nip every tendency to get too polished before it took over.

"When we started on the choreography, we initially went for a big band feel, with a flashy routine. We soon checked that. These people were coming from the sun, not Broadway. There had to be something kind of retarded about them."

Fighting perfectionism was especially tricky in the edit suite, where there were so many choices - particularly among the blue-screen takes. Several yellow people were shot in the same position, lit with hard directional lighting. Ayson spent a lot of time selecting the funniest and enhancing them in post-production so that they had an unearthly, sunburst glow.

The look of the yellow people was all-important. After dismissing such inspirational points as 1970s medieval retro and disco, the team zeroed in on a combination of bodily imperfection, wigs, over-tanned skin and yellow, over-stretched polyester. Closer inspection reveals a disturbing attention to detail.

"The theme was freaky, like your embarrassing uncle or aunt dressed in high pants from catalogues," says Ayson. "Clothes that highlight the abdomen a little too much. Man-boobs. And bras with too many frills and flounces that show through."

The moment when reality starts to return and the yellow people recede is a welcome relief: one of the actors sips his coffee, and starts to sing along to "Happy Mornings". He's found a way to tolerate the new day. But the yellow people have won.

"The client was very brave," says Ayson. "They'd laugh nervously and say, 'We're trusting you on this.' We were all going into a territory we knew nothing about."

Saatchi & Saatchi> http://www.saatchi.com
The Sweet Shop> http://www.thesweetshop.tv
Folgers> http://www.folgers.com