David Cameron has lost his temper with Ed Balls after the shadow chancellor teased him to "chillax, and have another glass of wine".
The Prime Minister dismissed Mr Balls as a "muttering idiot", only to prompt cries of "Flashman" - a reference to the bully in Tom Brown's Schooldays - from the Labour benches.
The taunt is a favourite amongst Labour MPs, who think Mr Cameron is at his weakest during Prime Minister's Questions when he is visibly riled and angry.
Sources close to Mr Balls claimed it was the shadow chancellor's demands for Mr Cameron to "tell us about the recession" that tipped the Prime Minister over the edge.
But according to MPs and political pundits on Twitter, Mr Balls sent the Prime Minister in to a spin by telling him to "chillax, and have another glass of wine".
The jibe is a reference to a recently published book which claims Mr Cameron unwinds from the stresses of his job by drinking three or four glasses of wine with Sunday lunch.
By the time it came to a Commons statement on the G8 and Nato summit in Chicago, Mr Cameron was in a conciliatory mood and volunteered an apology to Dennis Skinner after he urged the veteran MP Labour to retire during a heated Commons exchange last month.
The barbed remark prompted claims of "ageism" against Mr Cameron, who apologised to the 80-year-old Bolsover MP, admitting his remark was "sharp" and insisting Mr Skinner was a "tremendous ornament" in the Commons.
To make matters worse for the Prime Minister, former chancellor Lord Lamont, to whom he was a special adviser when Britain crashed out of the European Exchange Rate Mechanism in 1992, told the BBC's World at One, that Mr Cameron could be "quite volatile".
Mr Cameron's initial misdemeanour in PMQs was unexpected as he started to answer an innocuous question on the Government's economic record.