I've mostly traveled in European countries where people generally have a lot of experience with Americans and know, like every other nationality, some people are cool and some are jerks. I've seen a bit of ugly American behavior, but most Americans abroad I've encountered are traveling to learn, experience, and appreciate new cultures.

I sometimes ask taxi drivers, tour guides, and hotel and inn workers about positive and negative impressions they've formed from interacting with foreigners. Naturally they might not be up front with an American about negative experiences with Americans, but most I've spoken to have said most Americans they've encountered have been nice.

I heard plenty of complaints about Germans and the Chinese, though. Apparently, Germans tend to find fault with anything that isn't like what they have in Germany, and the Chinese don't make an effort to adhere to social norms and come off as rude.

As for the imperialist jerk you ran into, it doesn't shock me. What's shocking is how open he was about his attitude. I lived in London for six months and a few locals I met had a haughty, superior attitude toward foreigners in general.