These days traveling between EU countries is similar to traveling between American states. No visa, passport or border controls, same currency, people usually share a common language of some sort, somewhat similar population quantity and land area, lots of connected and common borders. It might be better to compare out-of-country travel within the EU with out-of-state travel within the United States. I suspect the data would be less titillating.
As for ugly American tourists, let me propose that any mass of culturally out-of-place tourists can be viewed negatively by the locals. Where I grew up we have lots of Japanese and Korean tourists (and now Chinese). A lot of us are equally annoyed by the ‘good Asian’ tourists as we are by the ‘ugly American’ tourists.