1. The don't of Thai social behavior are less clearly defined than those concerning the monarchy or religion, especially in a city like Bangkok where Western customs are better known and more widely accepted. However, what is acceptable in Bangkok may not be in the countryside where the old ways are still strong. Here are a few things to keep in mind:
2. Thais DO NOT normally shake hands when they greet one another, but instead press the palms together in a prayer-like gesture called a wai. Generally, a younger person wais an elder, who returns it. Watch how the Thais do it, and you will soon learn.
3. It is considered rude to point your foot at a person, so try to avoid doing so when sitting opposite anyone, and following the conception that the foot is a low limb: DO NOT point your foot to show anything to anyone, but use your finger instead.
4. Thais regard the head as the highest part of the body both literally and figuratively. As a result, they DO NOT approve of touching anyone on that part of body; even in a friendly gesture. Similarly, if you watch Thais at a social gathering, you will notice that young people go to considerable lengths to keep their heads lower than those of the elder ones, to avoid giving the impression of looking down" on them. This is not always possible, of course, but it is the effort that counts.
5. Public displays of affection between men and women are frowed upon. You may see some very Westernised young Thai couples holding hands, but that is the extent of the displaying of affection in this polite society.Losing your temper, especially in public, will more than likely get you nowhere. The Thais think such displays denote poor manners, and you are more apt to get what you want by keeping a cool head and concealing your emotions.
6. DO NOT be surprised if you are addressed by your first name; for instance, Mr. Bob or Miss Mary instead of by your surname. This is because Thais refer to one another in this manner, usually with the title "Khun" "(Mr., Mrs., or Miss) in front. Follow the customs of the country as far as possible and you will make more friends during your stay. And the more friends you make, the more you will want to return to Thailand.
Source : Tourism Authority of Thailand.