Because of two reasons, as I see it. Our government gets itself involved in world affairs that simply don't concern us. This generally kicks up a lot of dust and makes us look bad... because in that regard, we ARE. I don't like this about us. We go around the world like we're a third grader in the first grade sandbox. "Do it this way, it's MY world." That's a legitimate reason not to like us.
On the OTHER hand, there's our racist, bigoted, supremacist, idiotic, and generally assholeish minority that makes a LOT of noise, and has a LOT to say about what's best for us. Every country has these guys. It's just that because of point #1, OUR guys are listened to, exploited, and portrayed as the majority so that people won't like us.