Why are American girls (considered) crazy?

I've recently made friends with an African man. He is very polite and courteous in most instances, however, he has made it a habit to tell me American girls are crazy. I know we were raised in different cultures, so what I'm curious to know is what the main differences are between Zimbabwe's culture and American culture, as well as if any other cultures view American girls as crazy. I did pose this question to him, but he was either unable or unwilling to answer.