I don't know what you mean by "naughty," but the reason that locals in Prague are snooty is because the city is overrun with westerners who have seen too many Bel Ami videos and think they're going to roll in and sleep with a dozen models just because they're from the west. (BTW, most of the Bel Ami actors are not Czech.)

Plus, the Czechs are some of the most reserved people in the world, and their city is also overrun with Brits and Americans who think that the whole world should speak English. And they're much much louder than Czechs.

Czech people are actually really nice. They just don't react well to this dynamic, and if it was my home town, I wouldn't like it either.