How exactly is a nation arrogant? Does the nation have it's own conscience?
Is Russia crude? Canada feckless? China all-too-serious?
Repeated behaviors, once they become familiar those in close proximity to them, can become an attractive if they are interpreted have positive results, symbolically or materially. Often they spread through an entire population, usually over multiple generations, creating what we know as a "culture." Thus different populations often display different habits and morals.
Granted, you can't characterize every individual as embodying the type associated with the nation they belong to, but it is always a factor in their identity. For example, even if an individual Chinese person wasn't remotely seriously, if the entire body of their people tends towards seriousness, then that individual's relationship to his culture is subversive.
Subversion isn't always a bad thing, if the culture isn't worthwhile.
The United States has several bad habits, among them being, we encourage greed as a valid principle to order your life (rather than as an accessory to a spiritually ordered life that seeks to compress the numbers of its possessions to the fewest possible, while finding no less pleasure in these than it would in the acquisition of many others), the second being that we assert fame, for its own sake, as an ideal, to the expense of moderation and virtue, and thirdly, we deny our faults exist (both personally and as a nation) and don't take any responsibility for improving upon them.
Unsurprisingly, things aren't getting any better for us.