Whether you like it or not, you are a representative of the United States once you travel to a foreign country. Many have to come to associate such questions as: “Don’t you have an American cup of coffee?” or “You don’t speak English?” or “That’s not how we do things at home.” as typical American behavior overseas.
Nonetheless, there are several things you just can’t do when you travel as they are regarded in bad taste: taking photographs of people without asking their permission, acting critical or amused by customs that are alien to you, getting too familiar, too fast (for example, slapping someone on the back, even if the gesture is well intentioned).
To be regarded as a good ambassador (and save yourself from embarrassment), it’s advisable to read a few books or research online about the culture and customs of the country you plan to visit.
Clothing: Wearing shorts in public is generally not acceptable in most parts of the world, including some European countries. In Arab countries, low necklines, sleeveless shirts, and short skirts are definitely a bad idea. When in doubt, dress conservatively. Also, while it is tempting to dress in the local style, like wearing a sari in India, be sensitive to the culture – sometimes the local citizenry will appreciate your attempt to fit in; sometimes it will be considered an insult.
Greetings/touching: Handshakes are an almost universally accepted form of greeting, although in some countries, like Japan, a traditional bow from the waist down is preferred. Be careful how you address someone; don’t use first names unless you are invited to do so. In some countries, you’ll see a lot of hugging and kissing going on among the locals (Greece, Italy, Latin countries, Slavic countries); an affectionate hug or peck on the cheek that you share with a new acquaintance is fine, but usually if you are responding to, not initiating it.
Language/Gestures: Taking a crash course in the language of the country you will be visiting rarely results in the mastery of the language. Instead, learn some polite expressions (hello-goodbye-thank you) and relax. English is pretty common worldwide, especially in tourist areas, and you can always include body language to get your message across. However, some American gestures have totally different meanings in other countries. For example, in Bulgaria, shaking your head horizontally means “yes”; shaking it vertically means “no”. Also using the American gesture for “OK” (the thumb and forefinger making a circle with the other fingers pointing up) can be embarrassing. In Brazil that gesture means “screw you”: in Japan it means “money”: in Southern France it means “zero” or “worthless”.
Food/Drink: You may find yourself staring down at a local delicacy – snake soup in China, a yak burger in Tibet, sheep’s eyes in Saudi Arabia, calves’ brains in France – and wonder what to do, particularly if you are a guest in someone’s home. Be brave, take small bites, and pretend it tastes like something you like. When presented with a strong alcoholic drink, like ouzo in Greece, take small sips and stop when you must (you can refuse, citing medical reasons as your excuse). Remember that Hindus and some Buddhists don’t eat beef (the cow is sacred); Muslims don’t eat pork, and strict Muslims abstain from alcohol. If you are eating with Muslims, never touch food with your left hand (the left hand is for bathroom use and is considered unsanitary; using it would be very offensive).
Socializing/conversations: If you are acquainted with the history and culture of the country, you shouldn’t get unnerved. In general, some topics can be touchy or controversial, like money, religion, politics, and sex. But the particular nature of the people is critical. The Japanese do not want to talk about World War II; the French scowl at the classic American question: “What do you do for a living?”; the Chinese call their country “China” or the “People’s Republic of China” – not “the Mainland”; people in Scotland are “Scots” or “Scotsmen,” not “Scotch” (the drink) or “Scottish” (the language or the terrier).