I think that, American's as tourists are welcome and not judged individually. It's the Americans as a collective that are judged harshly for being Americans.

I think in locations that have heavy American visitors, yes we are treated differently, in fact I have experienced first hand.

Ansbach is a town in Souther Germany that has an American army base just outside of it. Many of the Americans living there are what you would call the "stereotypical" American. As a result the people in the town are not very nice to you if they know your American. Testing this theory when I lived there.. my husband speaks very fluent German. If we went to say dinner and I who speak German but not well, said nothing and allowed him to talk..we were treated very well, if I spoke we were treated very badly. A conversation at a later date at our favorite pub revealed from the locals this was not abnormal. He said, "The locals don't like Americans." he told us the only reason we had been so welcomed in the pub on our first visit (the reason we became regulars) was because the staff had taken us for being from Denmark or Sweden. When leaving Germany we were also offered first class seats for free as they had a cancellation after over hearing moments before the desk clerk telling an obviously American flyer that first class was sold out.

I also should add that though it may not be fair as not all Americans behave rudely in foreign countries.. by my witness 80% at least do, we've earned the harsh treatment.