I'm just coming back from a very long trips in the US. I've visited 16 states (+DC) in 15 days. It was really great.
There is still something weird when it goes about violence in the society in the US compared to France. Generally speaking, I would say all Americans, no matter their background, are a lot friendlier and social than we are in France. You guys are really nice dudes, especially in the South.
In France, we basically all hate each others, we constantly insult each others. We are indeed rude, that's not a myth, but it's not meant specifically towards foreigners, it's just our way of life. And it only went worse in the recent years. We have huge problems with our minorities, with our colonial inheritance, with out religious conflicts, with unemploment and the fact the country seems totally stuck. The social athmosphere is just unbearable, but despite that, for a reason I cannot explain, this doesn't result in so much killings.
In the US, it seems to be nearly the opposite. When meeting in the street, people are usually very polite to one another, but there are often very brutal and violent realities behind that. Police enforcement is particularly brutal in the US, the murder rate is much higher than in France. The disparity between wealth and poverty is particularly striking, and I would even say violent in its own way. But people remain polite and social no matter what.
It's really different. And quite weird.