As they were preparing to give their press conference at the G20 meeting in Cannes, President Sarkozy reportedly told the US president he “cannot bear” Israel prime minister Benjamin Netanyahu, adding “he’s a liar.”
“What about me?” said Obama, "I have to deal with him every day." Neither president knew their microphones were already live.
The comments were overheard by some French journalists, but only went public when a French website reported it four days later.
In many other countries, a private comment like that would have been splashed across the headlines almost immediately.
"I wondered last night what a group of French reporters was thinking in deciding not to report the candid comments," wrote journalist Ben Smith on the US website Politico.
“I find it hard to imagine [American reporters] wouldn’t have printed the conversations in a similar situation.”
When it comes to their politicians, French journalists have always been willing to draw a much thicker line between the private and the public sphere.
Where else could a head of state keep a second family on the go throughout his presidency without anyone finding out? François Mitterrand managed to pull that off for most of his period in office.
Rumours about the affairs of his successor, Jacques Chirac, were never made public. He was even nicknamed "3-minutes-douche-comprise", literally "3-minutes-shower-included", according to his driver who wrote a book about their time together.
In 2007, the two main candidates in the presidential elections, Nicolas Sarkozy and his Socialist rival Ségolène Royal, both gave the impression they were in stable relationships. Yet within just six months of the polls closing, both had broken up with their partners.
So why the secrecy? Is it that French people just aren't interested in what their politicians get up to behind closed doors?
Hortense Harang is a political consultant and heads up advisory firm Country Code. As a former journalist and a parliamentary candidate herself at one time, she has seen the issue from all sides.
"I think religion lies at the heart of it," she says. "The big difference is that we're not protestant. It was always the way that the Catholic church hid what popes were up to from the general public. Back then, the elite was the clergy, now it's the politicians."
She also sees a big difference between how the French perceive the link between private and public behaviour.
"In the Anglo-Saxon world the person is judged by how they behave in their private life. It's not like that in France. You can be one person at home and a different person in your public life."
"We have a schizophrenia. We don't think that because you cheat on your wife you will cheat on the republic. We just don't read as much into it."
So, are French people less interested in what politicians get up to in private? More high-minded?
"French people don't care. We all like a good gossip, but it's no more than that," she says.
The French certainly like a gossip and the country has a good number of celebrity magazines, ranging from the long-running Paris Match to newer entrants like Closer, but they tend to show more interest in film stars and pop singers.
Harang also thinks the French media culture has a big influence.
"In France we don't have a tabloid press. Tabloids can be terrible but they can also be a good thing for democracy because they push the big, traditional media to do their job and investigate. The style of journalism in France is more editorial than investigative. We like to tell people what to think rather than really inquire into the facts."
Privacy in France is guaranteed by strict laws. Article 9 of the Civil Code says that “everyone has the right to respect for his or her private life.” Courts have interpreted this widely to include relationships, health issues and the publication of unauthorized photographs.
As elsewhere, there is a public interest defence in France which can be used when private matters have an impact on public behaviour.
However, the likely expense of being on the wrong side of the law is a deterrent.
"Newspapers don't want to get into costly legal battles," says Harang.
The arrest of Dominique Strauss-Kahn in May on sexual assault charges brought private issues into the public sphere like never before in France.
Just two days after the former IMF director and one-time presidential hopeful was arrested in New York, journalist Christophe Deloire wrote an article in daily newspaper Le Monde titled "The strange omerta of the media in the case of DSK."
In the article he said he was amazed a 2006 book he co-authored about politicians and sex, called "Sexus politicus", had not received more attention. In particular, one whole chapter was devoted to Strauss-Kahn and his womanizing.
"The stories we told were not just about salon seduction,” he wrote. “The chapter led to intense pressure being put on us and our editor given the sensitive nature of the information.”
Yet, despite the revelations, the French media was "more than discreet," in Deloire's words.
Strauss-Kahn eventually had all charges against him dropped. However, the affair brought out revelations that had not been seen before about a French politician. Some people even spoke of a pre and post-DSK era.
Now that the dust has settled, does the DSK affair mark a turning point in how the media reports politicians' private lives? Will French politicians be exposed to the type of scrutiny that their peers get in other countries?
"I don't think so," says Harang, with a shrug. "What might change is that politicians will just be more careful.”