Well, the people who assembled yesterday were called together by the group Plane Stupid, the public places they arrived at were the Bolton and London homes of British MP, Ruth Kelly, and the unusual action was taken to protest the governments planned (and unpopular) expansion of Heathrow Airport.
In Bolton the "mobbers" played "airplane noise" at 56 decibels - the level deemed by the Department for Transport (DfT) not to be a nuisance to west Londoners - at 7.30am at the Transport Secretary's Docklands address.
A spokeswoman for London's Plane Stupid group, Elizabeth Baines, said: "It's incredible. Tucked away in her post London flat I can see now why it is so easy for Ruth to ignore the concerns of West London - the expansion of Heathrow won't threaten her quality of life."
She added: "London does not want more noise and air pollution. A decision in favour of BAA would be reckless cowardice - the UK can help beat climate change but not by doubling the capacity of the world's busiest airport."
In a separate demonstration a flash mob of between 50 and 100 protesters from anti-expansion group, The Heathrow Association for the Control of Aircraft Noise (Hacan), threw paper planes bearing a message and Ms Kelly's face at the DfT's Westminster headquarters.
Plane Stupid cites ten good reason for their opposition:
Aviation expansion will destroy ancient forests and woodland
Hundreds of acres of ancient oak woodland would have to be destroyed to make way for the government’s expansion plans.
Airport expansion will destroy important heritage sites
Across the country over one hundred historical buildings are at risk from airport expansion.
Aviation creates massive noise pollution
Living under the flight path is like living on a motorway.
Aviation diverts money away from public services
The airlines receive over £10 billion in tax breaks each year because of tax-free fuel and VAT-free tickets and planes.
Aviation is the fastest growing cause of climate change
Despite myths propagated by the airline industry, aviation already accounts for 13% of the UK’s contribution to climate change.
Aviation is mostly unnecessary
45% of air journeys in Europe are less than 500km – about the distance from London to the Scottish border.
Aviation's contribution to the economy is massively overstated
The aviation industry is only the 26th biggest industry in Britain.
Aviation expansion is wiping established communities off the map
At its seven airports across the UK BAA is proposing the biggest single programme of airport expansion that the UK has ever seen.
Airports cause illegal levels of nitrous oxide pollution
Heathrow airport is already breaching UK and EU legal limits for the high levels of nitrogen dioxide and therefore the present growth in the number of flights is probably unlawful.
'Cheap' flights are for the priviliged
It’s the rich who are really benefiting from the artificially low prices of air travel. The average income of people using Stansted Airport is £47,000 per year – and it’s supposed to be a budget airport!
Plane Stupid describes itself as a network of groups taking action against airport expansion and aviation's climate impact. Plane Stupid has no hierarchy or central leadership, but is instead made up of small 'affinity groups' who organise themselves. Inspired by networks like Earth First! and the mid-90s anti-roads protests, members take direct action against one of the root causes of climate change.
The following is from the Bolton News (UK).
Ruth Kelly's home is 'flashmobbed'
ACTIVISTS targeted the Bolton and London homes of MP, Ruth Kelly, to protest at the Government's backing of plans to expand Heathrow Airport.
Aircraft noise was played through the letterbox of her London Docklands apartment for 15 minutes at 7.30am yesterday until the protestors were reportedly chased away by her husband.
And later on, paper planes covered in images of the Transport Secretary and Bolton West MP's face, were flown into the side of the Department of Transport's headquarters.
Last night, a spokesman for Ms Kelly's department said: "Everyone has the right to make their views known and to protest, providing they do so within the law.
"The Government is currently considering the 70,000 responses to the Heathrow consultation in which everyone has had the opportunity to send us their views on our proposals.
"The Government expects to make a decision later this year after considering all the responses it has received to the consultation."
The protest started when six female activists from the Plane Stupid campaign group targeted Ms Kelley's London home. The group's Manchester wing also protested outside her house in Bolton at the same time.
The Flash Mob struck shortly before 11am when they turned up outside the DTI's headquarters in Westminster wearing red t-shirts emblazoned with the message No Airport Expansion'.
One of the organisers, John Stewart, of linked anti-expansion group, Hacan, said: "I am very pleased with this demonstration and it shows the strength of feeling about expansion."
The demonstrations were an attempt to influence Mrs Kelly, who is due to rule late this year on the building of a third runway at Heathrow Airport to cope with more planes.
They were attended by Liberal Democrat deputy leader Vince Cable, whose Twickenham constituency is below the flight paths of many Heathrow-bound planes.
He said: "Expansion would do much harm in terms of noise and emissions."
A spokesman for Plane Stupid said the peaceful demonstrations outside Mrs Kelly's homes had also gone well.
Elizabeth Baines said the group had left a letter for the MP with her husband, which read: "We do hope that you will keep this early-morning wake-up call in mind when you decide the future of Heathrow after summer recess.