Well, supposing some American chef blithely said that the Brits didn't know how to cook fish and chips, and that it took an American chef to do fish and chips right. Or suppose some American said all British beers were crap, and that only Americans made decent beer.
You'd probably think that person didn't know what he was talking about. And you'd probably be right, but what's particularly annoying to me as an American is I've known enough Europeans to know that when most of them here stupidity coming out of the lips of some European like that, they are just nodding along thinking they learned something.