some stereotypes about American people

The first week when I came to America, I found some American was noisy at night. I thought they have a party. I was very angry about those things. I don’t know why they are noisy. Before I come America my dad told me American is quiet and nice, but someone change my opinion. After that, my friends told me this is normal because it was Friday. American love to have a party in Friday. So, right now I can understand why they are noisy. This is the American life style. I think it is very different between China and American. Also, one time I was walking in the school at night, someone drove a car and he sticks his middle finger and say "fuck you boy" to me. I don’t know why and I don’t know this person. I was thinking is this is American conversation style? Maybe this guy just want to be funny, but I think this is a bad thing. Good news is this thing happen just one time. Finally, I want to say most American is friendly and nice. They help me when I needed help.