[ rùxiāngsuísú ]
= when in Rome, do as the Romans do.
dàng nǐ láidào wǒ de guójiā de shíhou, nǐ yāo rùxiāngsuísú.
When you come to my country, you should follow the local customs.
this has always been one of my favourite 成语 and it's totally true. So many of my friends had a really hard time in China because they kept trying to enforce their views on other Chinese people and saying things like "Well, that's not how we do things in England".