For instance, if you find yourself doing some drinking in Japan with others don't fill your own glass. Instead top off your neighbor's and wait for him to reciprocate. If you fill your own glass it's tantamount to admitting you're an alcoholic ("Hi, I'm Paul and I fill my own glass.''). In Russia, vodka is not for sipping; it's for shots. Women can get a pass on this one. If you're nearing the end of the bottle in Armenia, it's polite to empty it into your own glass; if you empty it into another's it obligates them to spring for the next bottle.
When you are out for dinner in France, never discuss money or try to split the check. Very uncool. In Japan, don't stick your chopsticks into a bowl a rice upright as that's the way they present offerings to the dead, and if you happen to be one of those people who just have to share their food with others don't pass the food from your chopsticks to another's --- it's reminiscent of a Buddhist funeral rite in which loved ones pass cremated remains from one to the other. And say you're dining in Mexico and you catch someone's eye? Say "provecho,'' or enjoy. Or they'll think you're one rude gringo.
In Greece, avoid waving to anyone with an open palm in greeting. For them, it's like flipping someone the bird. In Asia don't touch anyone with your feet --- does this come up much? --- as the feet are considered the "lowest'' part of the body; similarly don't touch anyone's head or tossle hair as the head is considered the spiritually "highest'' part of the body so the contact is a diss. If you refer to a Jamaican as a "native'' you might consider ducking from the punch that might be headed your way. Jamaicans view the term as laden with racial connotations and can be taken as a slur. Finally among the Thais picking the nose in public is not only permissible but is considered a sign of good hygiene. Wonder how they feel about flossing?
Leaving chopsticks upright in a bowl of rice is a clear no-no in Japan.