My impression, through the funhouse mirror of ... of... well, through a funhouse mirror, is the American tourists (it's all about the Americans anyway) are annoying because
1) They're American. That's a problem right there.
2) Loud. As in every one else is either deaf, the other Americans they're talking to are deaf or no one exists outside of their immediate conversational circle.
3) They _look_ loud. None of the colors match.
4) They smile like the idiots they are. Like they're 8 months old and just farted.