Nearly 3,000 people have joined Facebook group "Maggie's Good Riddance Party", which claims it will hold a "right jolly knees up" outside St Paul's on the day of Baroness Thatcher's funeral.
The protesters wish to "get their money's worth" from the funeral, which will be paid for in part by the state.
Those attending include a civil servant at the Department of Work and Pensions, a carer and a branch leader of the National Union of Students. Some warned of "civil unrest".
Police have said anyone wanting to hold peaceful demonstrations in London on the day of the funeral will not be prevented from doing so, but urged organisers to contact the Metropolitan Police in advance.
The protesters plan to line the streets where Baroness Thatcher's funeral carriage will pass, particularly outside the cathedral, so they can turn their backs on the coffin as it goes by.
Any protest, and ensuing confrontation with the police, will be watched by millions of television viewers around the world.
Lois Davis, a member of the group, advised protesters to stand along the funeral procession so "Thatcher's children" could turn away from the casket.
This would also make it difficult for police to "find a hotspot to kettle or disperse" because they would be dispersed along the route, she added.
The group is organised by Dominic Francis, a Oxford Brookes University student from Tunbridge Wells.
He said the protesters risked being likened to the Westboro Baptist Church, the American fundamentalist organisation that has picketed the funerals of US troops.
He said he was raised to "value compassion, love and forgiveness" and had some reservations about protesting. But, he said, Baroness Thatcher's role in public life meant she and her mourners had no right to be left in peace. He said he opposed Lady Thatcher for, amongst other reasons, opposing the re-unification of Germany and increasing VAT.
She was a warrior and she knew there'd be enemies.
She welcomed the fight and she knew how to fight and how to win.
Unlike the compromise crowd of this day. That's why they called her the Iron Lady.
Quote: Frank Cannon wrote in post #3Anyone notice that this human debris protesting a woman who turn the country around were not even born when she left office? I find it odd.
"The Republican Party doesn't demonize prosperity. We celebrate success in our party," he said. "And let me be clear, if Republican leaders want to join this president in demonizing success and disparaging conservative values, then they're not going to be fit to be our nominee."