Smiling works differently in different cultures. In France, for example, children are raised to wait until a social connection has been established before they smile. French people often say that someone walking down the street alone with a big smile on their face looks like an idiot to them. Not understanding this can make French people seem unfriendly to Americans and others from cultures where smiling is encouraged at all times.

I remember finding Barcelonans cold and abrupt when I arrived there after a week in France. A simple "¡Hola!" was an appropriate greeting. It felt rude at first, compared to the relatively elaborate greetings I'd grown accustomed to in Paris.

French people who haven't learned the cultural difference find American shop clerks extremely rude for failing to greet them and say goodbye. It really pays to learn this stuff before you arrive in a place with a different culture.