While it may be a contentious issue in the U.S. (10, 15, 20 percent? What exactly is good service?), tipping is outright taboo in some Asian countries. If you are eating out in Japan and South Korea, tipping is seen as an insult. In those countries, workers feel they are paid to do their job, and take pride in doing it well; no added incentive required.
OK, this doesn’t matter if you’re not visiting Central or South America. But if you are, saying that you’re from “America,” rather than the “United States,” is seen politically incorrect, as it implies that only the U.S. should be considered America, and that South America doesn’t matter. No word on what the Canadians think.
When wishing for good luck in the U.S. we cross our fingers. However innocuous this gesture may seem to us, if your are in Vietnam, this is like flipping the bird. Ditto for a thumbs up, which is considered the one-finger salute in the Middle East, Latin America, Western Africa, Russia, and Greece.