In some cases when I talk with someone from another country, he/she starts to talk badly about yet another country, which is neither my country nor my conversation partner's country. The content is usually a strong prejudice against the culture and people in the country, and could include racism.
This tends to happen especially in cases where many people in one country are reported to have negative impression on the country - Brits on Poland, Chinese on South Korea, Taiwanese on mainlanders, Vietnamese on Chinese, etc... In some cases I might feel that they start to talk badly about the country in part to attract my interest and/or feel sympathy, as they seem to know the majority of people from my country hate the country (and they likely had an experience of getting a "successful harmony" in the past but they would not know that people they talked with were racists).
However, I see it rather untolerable. Not only I don't accept their bigotries but also that I rather have quite a positive impression on these countries, and usually travel there frequently.
I usually get silenced and wait for them to finish their contempt. These people might be good otherwise (but not close friends and I don't see them as my friends, either), and not the kind of people I would like to bother to argue with. So how can I avoid it without asking it directly, which might possibly cause a tension?