Just ask Rammstein. (Sorry if anyone's already predictably linked to that, I haven't read most of the thread...)
People sometimes think their area doesn't have a culture for the same reason they think it doesn't have an accent: it's shown as normal in many other contexts, as certain American accents are used as the USA's default or standard on TV, or as members of the English upper class all speak the same way where ever they were born. An accent is a set of pronunciation patterns, so being used in lots of contexts can't make it any less an accent. In the same way, if a group of intelligent beings form a society it's impossible for it to not have a culture, even if it turns out similarly to or is adopted widely by others. I say impossible because even if a society had an extremely individualistic attitude with no traditions or behavioural norms or common identity beyond that of the land and government it shared - that individualism too would be a cultural characteristic.
While it doesn't have to be unique to meet the definition of 'cultural', if you want something that doesn't seem to have caught on anywhere else there may be this. I'm not aware of any other country that routinely uses knives and forks in which US table manners apply, e.g. swapping the knife and fork over, cutting with the fork, putting the knife down for most of the meal. I imagine it never caught on because, unlike most aspects of US life, which seem to place convenience at the front and centre, it appears rather clumsy and inefficient.