I lived in Japan for 20 years. The problem is that gaikokujin is too polite. Only dicks like Arudo Debito want to force everyone to use it, for reasons of political correctness, when in most cases the word gaijin is much more natural, and is not meant offensively. When Japanese people get to know you better they use your nationality as an identifier. Of course, the word gaijin is also used by gaijin to identify themselves.