I haven't met one in person(and I don't plan to),
Honestly, you probably have, and never knew it.
Everywhere I've gone, people have asked me... "So, you are from Britain, yes?"
but I read the news, watch TV, surf the internet, etc.
The pinnacle of the informed individual.
American culture is everywhere, and that's how they come across many times, unfortunately.
American culture is something of a misnomer. I haven't been to all 50 states - but I've been to more than most people, and traveled to three of the 'four corners' of our continent. The culture is different everywhere you go. There are some common things - but I've seen these in other countries, too. General hospitality is a human thing expressed in the more tight-nit areas of all societies (regardless of nationality).
Now, I'll be honest - many of my relatives are red-neck as hell (not necessarily in a bad way). We'd have our family reunion campout and stay for a few days in tents, RVs. We'd all hop in the back of a pick-up truck with some fishing poles and catch what we were going to fry up for dinner that evening. We'd sit around the camp fire and talk until midnight, swapping stories or what-have-you.
Go a little farther east into some of the more urban areas, and a family reunion is held over a single evening where someone in the family usually has a rather expansive home/estate, and everyone brings a main or side dish. Sometimes a hall or a part of a restaurant is rented out somewhere. ... And that assumes a family reunion is held at all (some people can barely trace their family back to their grandparents or their family is scattered across 10 states and 200,000 square miles).
I've never met a native Californian person - almost everyone seems to have moved there from some other state. The state, itself, is largely divided in both politics and society (southern and northern California are not exactly on good terms with each other). The people there tend to be fairly nice and more in line with those of urban communities... but their politics are absolutely alien to a midwestern boy like myself. There are a considerable number of laws and regulations that, to me, do not seem to make sense or be necessary. A number of the people seem to be in support of them, but I think a lot of them seem to think the rest of the country is a toxic waste dump, or something.
Most of us who travel abroad do not make a habit of bellowing: "I'm an American!" Perhaps somewhat ironically, while we try to be good stewards and to be good examples for our nationality... no one actually notices that we are American - they pass us off as some random European nationality.
Then I sit in the Mall of the Emirates and watch as a spanish Douche-o-matic comes in with his wingman, douchenozzle, and practically slams his crotch into the face of a girl (of the working class) hostessing for a restaurant while he tries to hit on her. My buddy and I both were about to make headlines of ourselves, but she handled it pretty well... still - it was like watching a fox evade dive-bombing hawks.
I see that stuff all over the place. It's not just Americans being the idiots around the world. There are just as many from other parts of it. The reason we catch the reputation for it is because we're the "big kid" on the block... and because we have 350 million people with a higher percentage of that population being able to afford international travel (or who can access it through various programs) - there are considerably more Americans abroad than that of most other nations (given that they have smaller populations).