I've only met two americans in my life so far, both were big, friendly and very open people. Something that struck me was as said before in this thread, their almost cripling lack of geographical and non american historical as well as present day knowledge.
It's almost as if it is deliberatly censored in the american medias.
Otherwise the rude obnoxious and loud stereotype I've found with the two I've met not to be true. Both were nice friendly though seemed totally lacking any form of humbleness. Not that they were disrespecfull just that they more than willingly boasted about their sucesses (Something that is almost conciderd social suicide here in Sweden lol).
That aside.. They weren't at all very different from us. Found it easy to socialize and hang out with both of them due to the shared media thing... well, as long as we kept to discussing american TV and american Movies and other thing related to america..