Opening a gift in front of the gift-giver - In Asian countries, such as China and India, opening a gift immediately upon receiving it is seen as being greedy.
Laughing open-mouthed - In Japan, laughing while exposing your teeth is considered extremely rude.
Tipping - While many countries have a suggested tip percentage, in Japan, while the service might be impeccable, tipping can be seen as degrading.
Eating with your hands - While it’s the norm to eat with your hands in many parts of South Asia and Africa, using utensils is a must in Chile, even if you're eating fries.
The "A-OK" sign - In certain countries this hand gesture is crude and offensive, and in places like Turkey, it is specifically offensive to homosexuals.
Peace sign -
In the UK, the backwards peace sign (palm facing toward your face) is equivalent to flipping someone off.
Thumbs up -
If you give a thumbs up in the Middle East, Latin America, and western Africa, it is the same as showing them your middle finger.
Altering food - In southern Europe, seasoning your food and dressing it in condiments is an insult to the chef. You are basically telling them that they did not prepare it well enough.
Blowing your nose - It is considered rude and even repulsive in countries including China, France, Japan, and Saudi Arabia to blow your nose in public.
Eating everything on your plate - In countries including China, Russia, and Thailand, clearing your plate is seen as a sign that you were not served enough to eat and are still hungry.
Jaywalking - In northern Europe, jaywalking is illegal, and the law is also strictly adhered to. Even when there are no cars coming, people wait for the crosswalk signal.
Revealing the soles of the feet - In Arab, Buddhist, Muslim, and Hindu countries, showing the soles of your feet is a sign of disrespect as they are seen as dirty.
Smiling at strangers - In Russia, a smile is seen as an intimate gesture, indicating a genuine affinity toward another person, so giving them out to just anyone comes off as insincere.
Crossing fingers - In North America, crossing your fingers is a gesture of good luck or a way of saying "I hope so!" However in Vietnam, crossed fingers is a crass gesture for female genitalia.
Patriotism - In many other countries and cultures, being overly nationalistic and proud of one's own country brings negative and still-raw reminders of fascism.
Asking what someone does for a living - Asking this question in the Netherlands is the same as asking how much money they make, and is seen as a classist question.
Not offering a beverage - In many countries, it is expected to offer visitors a drink when they enter your home, including anyone from a friend to the repairman.
Using your left hand - In Africa, India, and Sri Lanka, the left hand is seen as dirty, so using it to greet someone or eat is extremely offensive.