If you want to learn about the cultural differences between East and West, I recommend marry a Japanese woman. The other day I happened to place a (clean) pair of socks on the dining table as I was getting dressed, which resulted in a hailstorm of shock from my wife, who had never seen anything so scandalous. One of the most important concepts in understanding Japanese people is joshiki, or "common sense," the body of knowledge that everyone here magically seem to possess, except foreigners like me. In this system, things associated with the floor or the feet are intrinsically dirty and thus should never be brought into contact with clean things. If I spilled some milk on the floor, I'd probably reach for a rag to wipe it up then return the rag to the sink, but this would get me in hot water again: in the mind-set here, there must be different "levels" of rags for cleaning different things, with the cleanest reserved for wiping the dishes we'll eat off of, another for wiping things like the dinner table, and a third for cleaning dirty things like the floor. Some other things gaijin do that violate the joshiki system include washing shoes in the same washing machine you clean your clothes in, carrying paper money loose in the pocket rather than in a wallet, going skiing without buying $2000 of professional-grade equipment first and flying a kite at any time of the year other than New Year's Day.
An example of not using common sense. The joke is that the word for Emergency Exit is 非常口 which looks like it means "abnormal mouth" or in this case, abnormal knowledge, or lack of common sense. Which is what it would take for a guy to run into the girl's public bath dressing room.