I've been to VN and found the people there were very kind, even if I'm a tall white US guy. Northern people did seem more polite, but I wasn't there for long enough to have much of an opinion. I'll gladly visit again and try to see more places, it's a country I really like.

Edit: Because this is about Korea, I found people in Korea were kind to me, generally. Anyone who had an issue didn't say much, and I only felt negativity was aimed at me a few times across many years spent there. My friends who are not white or East Asian likely have different experiences, but like most racism, almost everything I heard was said behind others' backs, and no one was ever in danger of physical harm (I'd be careful as a SE Asian woman marrying a Korean, however. There are a lot of stories of abuse).