David Cameron was forced to apologise to Michael Meacher today, after he joked that the Labour MP had taken "mind altering substances".
During a high-charged PMQs session, Meacher suggested that Britain was now receiving less inward investment than Guatemala or Mali.
Cameron replied by making a joke about former Co-Op chairman Paul Flowers, who has been suspended from the Labour party for buying drugs.
The prime minister suggested the "mind altering substances have taken effect" on the Labour MP.
The comment saw Ed Miliband and Ed Balls quickly look at the Speaker for an intervention, with Miliband mouthing: "He can't say that".
As the session ended, John Bercow then granted Meacher a point of order.
"As everyone else in the House heard I asked a perfectly reasonable question. Is it parliamentary to respond by accusing another member of sounding as if he'd taken mid altering substances?" Meacher asked.
The Tory benches laughed at the Labour MP as the prime minister stood up to respond.
"I completely respect the honourable gentleman. I made a light-hearted remark. If it caused any offence I quite happily withdraw it," Cameron said.
The prime minister then said he was just trying to engage in some "light-hearted banter".
Despite the apology, the answer angered Labour MPs, who shouted "shame" at the prime minister as he left the Chamber.
The point of order capped off a strange PMQs, in which Cameron quoted from a critical tweet by former Labour MP Tony McNulty which was actually sent during the session.
Cameron spent much of PMQs trying to pin the blame for Flower's appointment at the Co-Op on Labour. The party is accused of knowing about his use of a work laptop to look at porn without warning the bank.
But asked if there should be an inquiry on the matter, Miliband focused on other matters.
"We've finally found an inquiry he doesn't like," Cameron said.
"If anyone has information they should stand up and provide it to authorities."
Miliband focused on comments by Nick Boles, planning minister, who said yesterday that the Tories had failed to detoxify the party brand.
"What he's really saying is this prime minister is a loser," Miliband said.