Nick Clegg has told Boris Johnson to focus on fixing London's housing crisis and transport system rather than throwing lewd insults at him.
The Deputy Prime Minister hit back after the capital's Tory mayor branded him David Cameron's condom during an interview.
Speaking on his regular LBC phone-in, the Liberal Democrat leader pointed out that Mr Johnson had issued the "prophylactic protection" jibe on Tuesday - which was his 47th birthday.
"This was on my birthday," Clegg joked. "I have had nicer birthday wishes than that, I can tell you.
"I do think that without sounding too pious we have all got quite important jobs to get on with and I think most Londoners listening to this would expect Boris Johnson to focus on the day job of sorting out our transport system, our housing crisis in London, rather than ever more exotic ways of describing his political opponents."
Clegg played down the importance of recent warm comments about him by shadow chancellor Ed Balls.
He said the idea the pair were paving the way for a post-election Labour-Lib Dem coalition was "completely ridiculous".
"I think Ed Balls confessed to the fact that he and I had a passing friendly conversation in the House of Commons," he said.
"If this is now being interpreted as some great act of political significance then we are reaching new levels of hype."
Clegg, who previously admitted that Mr Balls was the one politician he had personal animosity with, said they disagreed strongly on many issues.
"That doesn't mean you can't treat someone like a human being," he added.
Clegg said: "I am for once with Ed Balls on this. I think name calling is all very passe, all very 2013. I am going to say to Boris come on Boris, join Ed Balls and myself, let's have a truce."