I think the bad reputation has a lot to do with the rootin' tootin' shootin' sort of comments we hear from American politicians on TV all the time. US foreign policy seems to consist of: If it moves, bomb it; if it doesn't, bomb it till it does. (As long as the country concerned has oil, that is. We haven't heard much about saving civilians in Zimbabwe, despite years of slaughter and rigged elections. For their sake, I hope they find oil soon).
This doesn't leave a good impression on others.