The following is a first crack at an ostensive definition of 'American culture'-- things shared by the vast majority (let's say 90%) of native-born Americans. Many of these won't sound 'cultural' at all to Americans; they'll sound like just descriptions of the way things are. But each one of them would be contested in one or more non-American cultures.

[ American culture ]

I'm impressed with this list. I'd say it may even be closer to 95%. Of course there are a few that just don't apply to me, and a few that even I am unsure how the rest of the world works, but I think this is a good primer for the new folks, and for us Americans to remember that the truisms on this list aren't.