Perhaps
Due an an inferiority complex, it is important to instill the same upon others? Much as someone that is insecure always points out flaws in everyone else.
Perhaps Americans just stand out from the crowd everywhere as being loud and obnoxious because they are trained to see others as inferior and thus have to be louder and prouder than others, to express superiority.
I've seen it many, many times where, Americans accused of being too loud and proud, will retort with 'you wouldn't understand, we feel that way because America IS the best and we have freedoms and rights that we have fought for".
This not only illustrates arrogance and utter ignorance but also implies that the other nation just wouldn't comprehend what it's like to be proud because they have nothing to be proud of.
If you visit the UK, the people are the exact opposite in that they are self deprecating and will laugh at themselves before others. Brits call it being humble, I see it as the same as being comfortable in your own skin. Britain has fought for it's own freedom and rights more times than the US too. People just don't seem to have a need to express superiority, but there is a very strong, quiet and inherent pride in all Brits.
