Too loud and quite frankly they are just simple people, and do not appear to be very 'street smart'. This is based on my staying in many hostels throughout Europe the last 2 months. It is nine times out of ten Americans or Canadians who fail miserabely to fit in in any situation with other cultures.
The Americans you ran into were probably fuckings idiots and not well cultured. Most Americans are pretty knowledgable about cultures other than their own, and if they're not, then they're usually willing to learn. It's the europeans who are elitist shits that think anyone who doesn't look or act like them = bad apples. In America, almost everyone is respected, regardless of whether they're liked or disliked.
Europeans are snobby as hell. I live in NY and have ran into alot of these elitist fucks. Most of them think being knowledgable about obscure wine brands is what's important, along with skin color etc. Hierarchically speaking, Americans are one up on Europeans and everyone else.