Never cut the lettuce in salad because it's considered rude. Salads in France (and many other European countries) are meant to be folded up and eaten with a fork, not cut.
Good news for the tardy! It is considered inappropriate to arrive early or on time in most social circumstances. Always aim to be about 30 minutes late.
Don't bring yellow flowers to your host as a gift. In Bulgaria, they symbolize hatred.
Always eat your banana with a knife and fork. This custom dates back to the late 19th century, when a banana was viewed as an exotic treat.
Being disrespectful to bread (i.e. throwing it) is considered a sin.
In Germany, it is rude to cut potatoes with a knife. Instead, the Germans smash potatoes with their fork to allow more room for gravy.
Tipping after your meal has long been considered offensive to the Japanese, who think of getting tips as similar to begging. As more Westerners travel throughout Japan, though, this custom is becoming a little more lax.
Make sure to make eye contact with every person you clink glasses with during toasts. If you don't, they're convinced you'll incur seven years of bad sex.
You can throw bones or other inedible parts from your meal onto the table, if the table is covered with plastic.
In Tanzania, it is rude to drink beer straight from the bottle. The beer must be poured into a glass.
When it comes to pasta — and pasta only — don't wait for everyone to be served before eating; dig right in once you're served. For other dishes, you must wait until everyone receives their food.
When eating, it is always polite to have both hands visible. Otherwise, guests will assume you are playing with the legs of your dinner companions.
Never bring wine to a hostess. It is considered an insult.
Salting food is considered an insult in Egypt. The person cooking your meal intended for the food to taste like that.
Women aren't allowed to eat with a spoon.
It's customary to keep pouring tea into a cup until it spills over into the saucer.
Only eat with your right hand. Guests eat first and are seated farthest from the door. If bread falls onto the floor, you should pick it up, kiss it, and then raise it to your forehead before putting it back own.
Never doggy bag your meals. Either eat all of it at the restaurant or leave it.
If offered vodka, first flick a few drops in the air, "into the wind" (to the side), then on the floor. Then, touch your forehead with your finger and drink.
Make sure you slurp your udon noodle soup — they consider it the best way to make sure you're getting all the flavors of the soup in every bite.
Drinking vodka is part of everyday life, and not drinking is actually offensive.