The mildest form of ethnocentrism is simply defining the ways of foreigners as strange or peculiar. This is the basis of American jokes about the Korean practice of eating dogs. Another type of ethnocentrism is acting as though other cultures do not concern us, that we have no use for them. Americans show this kind of ethnocentrism by the fact that we rarely study and learn other languages, yet expect foreigners to know English. This sort of ethnocentric thinking is also apparent in the unwillingness of Americans stationed in Korea to learn about Korean culture and the refusal of American producers to customize their products for Koreans. The most extreme form of ethnocentrism is cultural genocide, wherein one culture finds the other so intolerable that it actively seeks to destroy it. This form of ethnocentrism was responsible for the Nazi extermination of millions of Jews in Europe during World War II. Closer to home, it inspired the killings of Native Americans and the confiscation of their lands by whites during the westward expansion. A final form of ethnocentrism is reverse ethnocentrism — the tendency to see the home culture as inferior to a foreign culture.