Common body language in the United States could mean trouble overseas. For instance, if you step over a person's legs in Nepal, you will be committing a big social no-no.
In most parts of Asia, the foot is more than the physical lowest part of the body. It is considered the 'lowest' part in a social sense also. Don't touch anyone's body with your foot. Don't prop your feet on top of tables or chairs and don't point to people or objects using your feet.
Just as the feet are the 'lowest' part of the body, the head is considered the 'highest' part. Don't touch a person's head in Asia and don't ruffle anyone's hair, including children. Also, one should never sit on a pillow that is meant to be used as a headrest.
In the country of Fiji, shaking hands throughout a conversation is very common. At minimum, a handshake can last a long time.
Heading back to Nepal, be sure to move your outstretched legs in so you do not, inadvertently, force someone to step over your legs. Also, give a wide berth to any monk's cushions when visiting a temple. And when walking around stupas or chortens, always walk in a clockwise direction.
Although it might seem contradictory, in Japan always wash before entering the water in a Japanese bath. Use a wash cloth to cover your private parts. Getting on a Japanese train requires a lot of pushing and shoving. Expect it and do it yourself.
Italian body language is very demonstrative. It is common for acquaintances to greet each other by kissing both cheeks. Hugs are common between men who are good friends, in addition to long lasting handshakes. Both Italian men and Italian women might walk side by side with their arms linked. Like getting on a Japanese train, pushing in crowded places in Italy is not considered rude. Do not be offended and do your best to hold your ground.
When in Russia, be careful of thresholds. Many people feel it is unlucky to shake hands across a threshold.
If you approached by someone in India who has their tongue between their teeth and motions with their hands like they are gathering the around around your head into their own space, do not be offended. On the contrary, this is a high compliment as the person is indicating that they find you incredibly beautiful or highly intelligent.
Ordering two beers in the U.K.? Don't do it like you do in the U.S. with your index and middle fingers up and palm facing towards you. This motion is highly insulting. Instead, turn your palm outward, like giving a peace sign.
After shaking hands in Morocco, touch your heart to show that you are taking the meeting seriously. Good friends greet each other with air kisses and a long stream of good wishes.