Don't forget fat.
Seriously though, I don't think Americans are stupid but I think the history education here isn't built well. Nobody puts an emphasis on history, and you don't even begin learning it untill after elementary school (some places even later). If people put knowledge about the world and its peoples at a higher importance, like they do with math for example, there wouldn't be a problem.
And there IS a problem. In a recent survey of youth from across the world about geography, the U.S. got 14th out of 15 (The 15th spot belonging to Mexico and the 13th to Canada). Only 89% of American youth were able to locate the United States on a map. To add insult to injury, 91% of Candians could accomplish the same feat. It should also be noted that more Americans knew where last years season of survivor took place, than where Iraq and Afganisthan were located. Did I mention that a large percentage of American kids think Germany was our ally in World War II?
I don't think Americans are somehow less intelligent than countries like Sweden (who got 1st place in the above mentioned survey). But as someone who knows a bit of history and who's going through these history classes here, I have to say that there's a lot of things that could be done to improve them. The current system produces a few intellectuals, many average people, and a good share of idiots who help spread the American stereotype. The fact that this image is trumpeted by pop-icons such as Jay Leno or Homer Simpson, doesn't help the case.