Natto (納豆) is perhaps the most controversial dish in all Japanese cuisine. It's made of soybeans fermented with a particular bacillus and then eaten, usually for breakfast with rice, mustard and Welsh onion. Because its taste and texture is somewhat peculiar, many Japanese think of it as the absolute gastronomical test for non-Japanese: when discussing food with the Japanese one of the first things a non-Japanese will be asked is if they can eat natto; very often they will reply "no" and the Japanese will be happy to see another stereotype confirmed. On the other hand, I have never seen anyone, Japanese or non-Japanese, buying natto at the super-market and whenever I've stayed at a hotel with a breakfast buffet, I've rarely seen it picked by more than 1% of the guests -this leads me to believe that its an acquired test regardless of one's skin color. For the record, I don't like it either although I can eat it.
(For a bigger version of this picture both in color and black and white, check my "Japan Arekore" set on Flickr)