Why do Americans make fun of the rest of the world?

Why do Americans have a tendency and an inclination to make fun of the rest of the world. They ridicule British people about their bad teeth and when they talk about French, they say " French people stink! ". Rightfully, the truth of the matter is completely the opposite. According to the International survey, the British are way ahead of the Americans in dental care and oral hygiene. And, French people use more soap and perfume per capita than Americans do. It appears the French are ahead of Yankees in hygiene but they keep it to themselves, and they never brag about this particular issue. However, Americans, always consider themselves to be "the best" and almost always make fun of the French, the British, the Mexicans and/or the rest of the world. Why is that?!

Please make your comments in ENGLISH. (Merci!) Thank you!!