It is not just polls. It is difficult to escape the conclusion that US-ers, especially males, tend to be arrogant, mean-spirited, and violent people. Not all, of course, but a visibly larger share than in other countries. And that tends to cut across all ethnic and class lines. A particular characteristic of this trait is its bipolar character - the superficial politness that can turn into a violent rage in a matter of seconds. For example, Europeans can be rude if you step on their toes, but that is as far as most of them will go in most conflicting situations, and they are also more likely to express a variety of more nuanced emotions. Here, otoh, people are sugary proper in most every day interaction, but when things do not go their way, eg. someone cuts them off in traffic or expresses opinion they disagree with, they are more likely to go ballistic and blow off their tops. An the the acceptance of violent, arrogant and vindictive behavior in conflict situations (even among those who usually do not engage in such behavior) tends to be higher here than in Europe.
This is precisely the point Michael Moore tried to make in _Bowling for Columbine_ by contrating US-ers and Canadians.
Wojtek