Although the Japanese generally are very polite and considerate, there are times when foreigners like me might consider what they do to be rude. First of all, the Japanese love to read over a person’s shoulder, and if you’re typing something in Japanese on a laptop, well, don’t be surprise if a crowd gathers to read what all the interesting things this gaijin is typing — it’s just not considered rude by them. My mother taught me not to reach over people’s plates when eating dinner together, but to ask for someone to pass the item to me; apparently the Japanese didn’t get that memo, as it’s common here to reach across the table to get what you need while eating. Similarly, Americans don’t usually drink soup out of bowls, however picking up the bowl and drinking deeply is the accepted way to enjoy miso soup, ramen and so on. Oh, and while eating any noodle dish like ramen or soba (note, not spaghetti!), you’re expected to slurp your noodles as loudly as possible, and not doing so will likely elicit comments from everyone around you.
People will ask what’s wrong if you don’t slurp your noodles.