Labour has accused David Cameron of sexism after he told a female MP to "calm down dear" during a Commons exchange.
The prime minister borrowed the catchphrase made famous by Michael Winner, during a row about NHS reforms.
Shadow chief secretary to the Treasury Angela Eagle, at whom the comment was aimed, said "a modern man" would not have "expressed himself that way".
But a Downing Street spokesman said it was just "a humorous remark".
The clash came as Mr Cameron used the words of former Labour MP - and GP - Howard Stoate to defend his plans to introduce GP commissioning in the NHS in England.
Dr Stoate, who stepped down at last year's general election, wrote in the Guardian that discussions with his colleagues revealed "overwhelming enthusiasm for the chance to help shape services for the patients they see daily".
But it was Mr Cameron's suggestion that Dr Stoate had been beaten during the election that riled some on the Labour benches.
Amid shouts of "he stood down", Mr Cameron paraphrased the famous car insurance advert starring film director Michael Winner: "Calm down dear, calm down, calm down."
Shadow chancellor Ed Balls could be seen challenging the remark and pointing to Ms Eagle in the Commons - Mr Cameron replied: "I'm not going to apologise, you do need to calm down."
Speaker John Bercow had to step in to quieten the Labour benches, telling MPs: "There's far too much noise in this chamber, which makes a very bad impression on the public as a whole."
But Labour MP John Woodcock stoked up the row later, telling MPs the prime minister was "losing his rag because he is losing the argument".
BBC News Channel chief political correspondent Laura Kuenssberg said Labour MPs reacted angrily to the remarks, with one saying: "It's pure Bullingdon Club" - a reference to the exclusive Oxford University society of which Mr Cameron was a member.
Labour's deputy leader and former equality minister Harriet Harman said Mr Cameron's "contemptuous response" to Ms Eagle showed "his patronising and outdated attitude to women".
"Women in Britain in the 21st Century do not expect to be told to 'calm down dear' by their prime minister," she said.
Ms Eagle told the BBC: "I don't think a modern man would have expressed himself that way. What I was trying to do was point out that he had got some facts wrong."
Labour has called for Mr Cameron to apologise, but Ms Eagle said: "I think if there's an apology due it should be for the dreadful growth figures that we have seen today."
Asked if she had felt patronised by the remark, she added: "I have been patronised by better people than the prime minister."
But the man who made the catchphrase famous, Mr Winner, told BBC Radio 4's PM programme: "I think the prime minister's terrific, he's got a good sense of humour, he's using a phrase which I introduced to the nation and which people use all over the place, and why shouldn't he?"
The director, who has supported both Conservative PM Margaret Thatcher and Labour PM Tony Blair in the past, said Ms Harman was "a nice person but she's going over the top - what planet is she on?" and said Labour should "get a sense of humour".
Lib Dem Chief Secretary to the Treasury Danny Alexander defended his cabinet colleague Mr Cameron.
He told the BBC: "If it has caused offence, obviously that was not right and I hope it hasn't caused offence... because it was a joke."
Mr Alexander added that he had thought the remark was directed at Mr Balls, who liked to "chunter from the front bench".
A Number 10 spokesman told reporters: "It was a humorous remark.
"They [Labour] will do anything to avoid talking about the economy after the good growth figures."
At the last prime minister's questions before the Easter break, Mr Cameron sparked a row with Labour after calling Mr Balls "the most annoying person in modern politics" during noisy exchanges.
He has also used the "calm down dear" line before in the Commons - directing it at then Foreign Secretary David Miliband in 2007, while responding to a statement on Afghanistan being made by then PM Gordon Brown.