Well, the emphasis of German things was indeed a joke. I simply assumed you'd have a sense of humor to handle it, as I myself often face American stereotypes as much. If you're not comfortable with it then I'll refrain from the wisecracks about German origins. All you simply had to tell me was you were uncomfortable with it and I would stop, as I'm doing now.
Again, I apologize if they offended you as I did not intend them to be insults.