What is the polite way to address Thai people?

M：So what kind of things would a visitor to Thailand need to know about? Are there any social customs that are different from a European country?
W：Yes, there are a lot of things that are different. For example, the names, the way you address people is different.
M：How is that?
W：Well, you always call people by the first name, the polite way to address people is by their first name.
M：What, even in a formal situation?
W：Yes, you say "khun"—it’s like "Mr" or "Miss" , or "Mrs".
M：You mean it’ s the same for men and women?
W：Yes, it’ s the same. You say "khun and the first name, and also, when you meet people, you don’t shake hands usually. There’ s a traditional greeting called a "wai".
M：A “wai” ? What’ s that exactly?
W：Well, you put your hands together, like when you pray, and you bow your head forward slightly, and the other person does the same. But it’ s not usually for friends. You needn’t to do it. You just do it for people older than you.
M：I see. And in public are there any things that you find different? Is it true that it’ s not acceptable for a young couple to hold hands in public?
W：Nowadays some of them do, maybe because of the influence of Western society, but it’ s not so common. Another thing that people might find very different is that the head is very important for Thai people—you can’ t touch another person’ s head. You have to respect people. As the head is the most important part, the feet is the lowest part. It’ s rude to point at anything with your feet. And you also can’ t open a door with your foot.