Boris Johnson and his Canadian counterpart Justin Trudeau mocked bare-chested Russian tyrant Vladimir Putin at a crunch gathering of global leaders.
The two prime ministers joked about the Russian President at the G7 summit in Bavaria, Germany, where the sun shone and the mercury topped 28C.
As leaders greeted each other, Mr Johnson asked if he should keep his jacket on, and then said: "Shall we take our clothes off?"
He added: “We have to show that we’re tougher than Putin.”
Mr Trudeau quipped “bare chested horseback ride” in a reference to infamous pictures of the Kremlin despot shedding his shirt for a hack in the mountains.
Mr Johnson then could be heard, saying: "We've got to show our pecs."
European Commission President Ursula von der Leyen added: "Horseback riding is the best."
Labour MP Chris Bryant, a former Foreign Office Minister who sits on the Commons Foreign Affairs Select Committee and chairs the All-Party Parliamentary Group on Russia, accused Mr Johnson of “childish narcissism”.
He told the Mirror: “He’s an embarrassment and I think he’s slightly deranged.
“There comes a point at which your narcissism and your hubris are so flagrant that you become a national embarrassment.”
Independent MP Neil Coyle, who also sits on the Commons Foreign Affairs Select Committee, said: “If Johnson doesn’t take a G7 seriously then what’s he still doing in office?
"It might be a joke to him but Putin’s instability is a cause for international concern.
“There doesn’t seem to be a need to go out of the way to deliberately provoke him.”
Lib Dem foreign affairs spokeswoman Layla Moran said: "Boris Johnson has yet again proved that he is a national embarrassment who is completely unworthy of representing Britain on the world stage.
“Families across the country are struggling to make ends meet while Johnson jokes around abroad.
"These are the bizarre ramblings of a man not thinking straight because the pressure of his failing leadership is getting to him.
“The fun and games are over for Boris Johnson."
Mr Johnson later suggested that Russia might not have invaded Ukraine if Mr Putin had Tory backbenchers on his case.
In an interview with CNN, the Prime Minister was asked about his message to Tory MPs, who say "he is a drag on his ticket".
He said: "I think the great thing about democracy is that leaders are under scrutiny and that I do have, even though you say I got things going on back home, that's a good thing. I have got people on my case, I have got people making arguments."
The PM added: "Do you really think that Vladimir Putin would have launched an invasion of another sovereign country if he'd had people to listen to properly... arguing, if he'd had a committee of backbenchers, the 1922 Committee, on his case?"
Earlier, Mr Johnson and Mr Trudeau also bantered about the size of their official aircraft in talks on the sidelines of the summit.
Mr Johnson told the Canadian premier that he spotted “Canada Force One” on the Tarmac at Munich Airport when he touched down this morning from the Commonwealth Heads of Government meeting in Rwandan capital, Kigali.
“Can Force One”, as the plane is known, is an Airbus A310 categorised as a CC-150 Polaris.
Mr Trudeau joked that Mr Johnson’s Airbus A321 plane was bigger - to which the British PM insisted his jet is “very modest”.
The Tory leader has been forced to use the smaller of his two planes because Prince Charles was using the Airbus A330 RAF Voyager to fly to Rwanda, because of protocol.
The Voyager was converted from a troop carrier and air-to-air refuelling tanker to be used by the UK PM and aides on foreign trips.
The revamp cost taxpayers £10million - and when Mr Johnson entered No10 he demanded a £900,000 paint job to switch the aircraft from military grey to patriotic red, white and blue.
