The prime minister has had a dinner-time row with the Argentine foreign minister after he brought up the Falklands over dinner.
Hector Timerman raised the issue of the ownership of the islands during a meal-time meeting between EU leaders and Latin American representatives.
According to Argentinian media, he said: "The Argentine government expects countries from the European Union to support the United States resolution that urges Argentina and the UK to dialogue over the Malvinas Islands."
Mr Cameron demanded to be allowed to respond even though it wasn't his turn to speak, saying "everyone has the right to self-determination".
He also argued that it was "totally inappropriate" for Argentina to be "threatening" investors in the area, according to Downing Street.