A post on "What Japan Thinks" which offered survey results about what sort of chopstick-related faux pas people notice got me thinking about western table manners and about how and why such rules come about. If you read through the list in the "What Japan Thinks" article (and I recommend you do so as it's pretty interesting and information), some of the "violations" seem relatively arbitrary and, in my opinion, inoffensive.
To some extent, I believe what constitutes bad manners at the table is related to considerate and sanitary behavior. For instance, being pointed at with cutlery of any sort isn't a comfortable experience as it brings to carries a hint of someone attempting to gut you with a salad fork or scoop out mushy body parts with a spoon. Allowing your eating implements after they have been in your mouth to touch any communal dishes or spaces transfers your cooties to everyone else.
Some rules, however, seem very strange things to consider poor manners such as "eating one dish continuously." Why should others care if you eat all of one dish before consuming another? In the west where people serve themselves from a large dish placed in the center of the table, this may be considered a problem because someone might be consuming more than his fair share of a select dish. In Japan, where food is generally served to each individual in separate dishes (unless you're at a bar or pub), you're eating your own portion and not taking away from a community platter.
The interesting thing about manners and food-related behavior is that, if you look at the etiquette across cultures, you can find a lot of conflicting ideas. In fact, sometimes you can find that ideas conflict within the same culture. One of these points in the U.S. is about whether or not you leave food on your plate. My family, and this is probably because we were poor and food was not to be wasted, always insisted on cleaning ones plate. In other parts of the U.S., it's perfectly fine to leave food on your plate if you're not hungry enough to eat it all. In fact, some people consider it bad manners to eat everything because it makes you look piggish. In Japan, while I don't believe it's bad manners not to finish what you are served, it makes your host believe you didn't enjoy the food.
One of my students decided to prepare a simple Japanese meal for her host family during a home stay. Before she left, she asked me what she could prepare and I told her that it really depended on the people. Some people are pretty open-minded about various types of food and some have limited palates. I recommended she consider some sort of nabe or Japanese stew. She opted to do a simpler sliced beef dish which was mainly based on seasoning with salt and soy sauce and served with rice. The homestay mother praised the dish, the son openly disliked it and no one cleaned their plates. She assumed that none of them liked it because they didn't eat it all. While it's possible that the family didn't like it, it's also possible they just aren't the sorts to clean their plates. When I explained this to her, I don't think she actually believed me.
Fortunately for foreign folks, the Japanese forgive us all our failings in terms of manners when we are their guests. They don't expect us to know enough not to leave our chopsticks sticking straight out of our rice (which is actually one of the nastiest things you can do as it relates to funeral practices) and tend to be impressed if we are proficient in using chopsticks at all.