There are many, many, many things that are only associated with Japan that are incredibly popular, for good reason and they need to be shared with the world. But there are some things, of which we completely missed the point.
One of the first things that come to mind when thinking of Japan, sushi. Words cannot describe just how badly we managed to screw up this. In Japan, sushi including, beef, chicken, vegetables, prawn, cheese, anything teriyaki and anything tempura, is considered a bit weird or wacky. The main thing you will find is raw fish. The idea of sushi is western eyes is great up to the point of eating raw fish, which is what basically sushi is!