Each country has it’s own customs and superstitions regarding dining etiquettes

China
Slurping soup isn’t frowned upon; it’s considered to be a sign of culinary appreciation.

A traditional seafood superstition is that it’s bad luck to ever turn a fish over on the plate. Doing so is thought to cause the boats of fishing families to overturn out at sea. When fish dishes are served, the fish head is always reserved for the guest of honour; the platter holding the fish will always be turned in such a way that the fish head points toward this guest. The fish’s eyes and lips, though, are considered the “most valued delicacies,” and are offered to the eldest lady present.

France
In France, the custom of giving the lady the “good seat” (the bank/chairs with their backs to the wall, while men face the lady and the wall) is more strictly observed. I’ve been really surprised by how many fellows – even men on dates! – in Canada and in the U.S. stick the gal in the “bad seat”.

In the south of France, superstition has it that if a woman is tossing a salad and leaves fall out of the bowl, she’ll become pregnant the next year.

Germany
When dining or drinking with Germans, guest should wait until someone says “Guten Appetit” or wants to “anstossen” (click glasses to toast). It’s considered offensive not to make eye contact when toasting (this is justifiably the case in many countries.)

Hungary
One of the most popular Hungarian toasts is ’égészegedre!’ It’s wise to check pronunciation in advance, though, since the way English speakers typically pronounce it has the toaster enthusiastically saying “To your ass!” instead of “To your health!”

Italy
When Italians are served pasta, they typically won’t use (or be served with) a knife or spoon; they simply twirl the pasta on the side of their plates.

Espresso is always enjoyed after the meal, never with the meal, and is usually ordered following dessert, not with it.

Japan
Many chefs in Japan are pleased when diners slurp their noodles as loudly as possible, since this is taken as expressing delight in the dish.

It’s considered very, very bad etiquette to pass food from one set of chopsticks to another person’s chopsticks.

Middle East
In many Middle Eastern and Arabic states, women are not permitted to eat with men. In some homes, women may eat in the same room, but off in a corner with the children, the reason ostensibly being that no one is permitted to see a woman unveiled other than her husband. In other homes, women remain in the kitchen to cook and serve, and then eat whatever is left over.

Russia
During Russian celebratory dinners, diners will more often than not use solely their fork or fingers.

The drink of choice at many dinners is usually vodka, closely followed by champagne, which can be served at the same meal. Enjoying vodka with meals in Russia doesn’t have the same stigma that it would in the U.S.; it’s part of perfectly respectable mealtime celebrations.

UK
Smoking in Scotland is frowned on during dinner, and at formal occasions, is considered a big no no if done before toasting the Queen.

I found this funny bit regarding tea on a British site: “If you are a Brit who wants a good cup of tea in the USA, ask for a cup of hot water and bring along your own tea bags. They never make it strong enough for the British palate because they never use boiling water.”

Sub-Saharan Africa
Eating with the left hand – ever – gives great offense at the table (the left hand is considered to be the unclean hand).

Thailand
Meals are often shared around a low table, with diners sitting on the floor. Pointing the soles of feet at anyone while at the table is considered a grave insult. (Diners remove their shoes before entering the room, and know never to step on the room’s threshold.)

The head is considered the most revered part of the human body, and touching it at the table is strictly taboo. Diners know not to touch the heads of their host’s children, and to keep their heads lower than any images in the room of the King, Buddha, or other religious figures.