One of the many clichés about Germany and the Germans says that they act in a not very friendly or even rude manner towards strangers. You might get that impression when you first come to Germany and try to get to know somebody else on a train, a bar or at work.
Especially as an American, you might be used to getting in contact with strangers really quickly. In Germany, you probably won’t. It is a scientifically proven fact that German people simply don’t chat in public places when they don’t know each other. But what is often interpreted as rude manners, is more like a basic inability of Germans to small talk – they simply are not used to it.