@Melodyzhong,
Please, I'd like to suggest you to start saying "PLEASE" and "Thanks". saddly, many Americans do not say these important words, it is like they are "démodé" ( and certainly they are not). This is a sample of culture conflict between America and other cultures, the immediacy of things, the demanding way that thinks the world gravitates around America...
I love this country and the people who make it. However, it still shocks me to see how common this lack of politeness is present among many fellow Americans: sad.