okay I think I help you there. if you speak to any Vietnamese without letting them know that you are Chinese, they will quickly reveal themselves. the Vietnamese almost down to last man, woman and child are obsessed about that fact that Vietnam was once a province of China and they obsessively paranoid that China wants it back. if you read Vietnamese bloggers you'd really want to laugh, they are even more ridiculous than reading nazis talking about the jews. there was one time that some pigeons escaped and flew across the border, and the Vietnamese netizens said that China has sent birds with spy cameras.
which is totally ridiculous: if you look in history, after Vietnamese independence in the 970s there were only 5 wars between China and Vietnam
1st, Song dynasty, started by a Viet General plundering a Chinese village
2nd, Yuan dynasty, Viets refused to let the Mongols pass through to Southeast Asia
3rd, Ming dynasty, Viet General rebelled against his own king, then ambushed and killed the Chinese ambassador
4th, Qing dynasty, Viet king asked China as a tributary for help after getting overthrown by rebels
5th, P. R. , Viets attacked Cambodia which China was required by treaty to protect
but it makes them feel important to think that China is interested in them.