An interesting example of the different meanings of body language is eye contact. In the US and in many parts of Europe, direct eye contact is considered as a means to express interest, to indicate trust in the other person and to convey openness. "Look me in the eye, I'm honest, I'm not a liar"' are some of the interpretations of eye contact.
However, due to religious reasons, eye contact is a dangerous thing in Muslim countries. It's offensive for a man to look a woman in the eye or even to glance at her in a more than cursory fashion. The same applies to Asia, where eye contact is considered impolite and an invasion of space and can cause the opposite reaction to what a visiting foreigner intends. As far as Asia is concerned, prolonged eye contact is a challenge, an aggression and a battle of strength and power.
Whereas in South America, eye contact between opposite sexes can be interpreted as an invitation, longer eye contact or staring between women is often understood as criticism of the other woman's appearance.
American and Southern Europeans tend to be more physical. Men who greet each other with a handshake and a slap on the arm or the back, are just being friendly. Asian countries, especially Japan would consider such behavior aggressive. In some Islamic countries, handshakes are much less common. Whereas in the US and Europe, a firm handshake is appreciated and a limp one not looked upon favorably, a firm handshake in Turkey is considered rude and aggressive. In some African countries, the limp handshake is the thing to do.
Thumb and index finger, forming a circle with the hand raised, is the universal American sign for "OK" or "I agree" or "excellent". The same sign however has a vulgar meaning in many South American counties, especially Brazil and may provoke an aggressive reaction. In Spain, it's a sign for cuckold, certainly not appreciated by the person who is the recipient of the signal.
An interesting sign with very different meanings is the 'fig sign". The thumb is poking out between the index and middle finger. In ancient Rome it was a sign for good luck and that meaning has survived in Portugal and Brazil. But in many other countries, as far spread as Indonesia, Turkey, Greece or modern Russia, it's a very rude signal, meaning "screw you".
Hand thrust out, palm upward and outward is in America and many other countries understood as a well meant warning, in the sense of "stop", or "danger". But if you travel to Greece, beware! If the fingers are splayed, you are in the presence of a sign known as "moutza", which is an extremely offensive and aggressive gesture. Curiously, the signal has the same meaning in Pakistan.
Needless to say, that given the diversity of interpretations which can turn friendly gestures into the opposite, it's a prudent approach to familiarize oneself with the different meanings when traveling and to keep gestures to a minimum to avoid giving offense.