The phenomenon, sweeping the United States and Europe, uses the Internet to organise a crowd which appears suddenly, performs a pre-arranged mass act and disperses as quickly as it came.
Staff at yesterday's chosen target, a Burger King outlet, quickly prepared extra food for the sudden influx of supposedly hungry customers.
They had 100 buns under way, along with 10 chickens, eight baskets of fries and four trays of meat patties, before they realised no one was ordering.
"We saw a whole lot of people coming in so started preparing - then no one ordered," a staff member said.
The flash mob invited people to register their interest - and their e-mail address - on the website http://www.flashmob.co.nz
They were told to meet at Aotea Square at 12.45pm and look for a man wearing a parka with a bull's-eye target on the back.
To him they were to say "good afternoon Monty" while tapping their nose. He would then give written instructions on what to do next.
By midday, giggling punters, most of them apparently in their 20s, started gathering.
Final instructions from Monty, who identified himself only as a Waiheke Island student in his early 30s, were to move immediately to the lower Queen St Burger King.
"Stand in front of the till and avoid eye contact with the staff," the note added.
"Frown at the menu as if you are deciding what to order, occasionally pointing to an item on the menu ... but do not order anything.
"At 12.50 we should all be present. Start mooing like a cow. All different kinds of moos. But continue to look as if you are considering the menu.
"At 12.51 smile at the staff and give them a huge round of applause and cheer!
"At 12.52 leave quickly and return to the matrix and your normal life."
And that's exactly what happened, amid an atmosphere part-nervous tension, part-excitement. And a few minutes after the mooing started, the restaurant was empty again. Staff were left dumbfounded.
The manager on duty did not want to be named, but said the extra food had to be discarded. Senior staff at Burger King's head office could not be contacted.
Monty said he intended no trouble for Burger King. "I'm going to send an e-mail out to all those registered with flash mob, encouraging them to go in and place a real order this time," he said.
So why set up a flash mob?
"There's so many depressing issues happening in the world today that people are screaming out for fun things like this."
Another would take place in Auckland before the end of the month, and Monty promised a "very silly summer season".
Futurist Howard Rheingold unwittingly inspired the flash-mobbers with his book Smart Mobs: The Next Social Revolution, which examines how technology redefines social interaction.