Ask them to name what countries China has invaded.When they say "tibet" tell them that tibet was part of China for over 1000 years and they reaffirmed in a treaty that it was part of China after the revolution. When they say Xinjiang tell them that was part of china 2500 years ago.If they say Hong Kong or Taiwan inform them that nobody disputes that those are part of China and they haven't even used military force to make them reintegrate under the Chinese system of government.When they say "the south china sea" you say that the RoC fascists who lost the civil war, signed the treaties defining the maritime zones of China when they controlled the China's UN seat, despite the fact that all they controlled was Taiwan.