-The Monarchy : Thai people have a deep, traditional reverence for the Royal Family, and a visitor should be careful to show respect for the King, the Queen and the Royal Children. It is a criminal offence to make critical or defamatory comments about the King or other members of the Royal family, punishable by a sentence of 3 to 15 years.

-Religion : Visitors should dress neatly in all religious shrines. They should never go topless, or in shorts, hot pants or other unsuitable attire.
It is acceptable to wear shoes when walking around the compound of a Buddhist temple, but not inside the chapel where the principal Buddha image is kept. Each Buddha image, large or small, ruined or not, is regarded as a sacred object. Never climb onto one to take a photograph or do anything which might indicate a lack of respect.
Buddhist monks are forbidden to touch or be touched by a woman, or to accept anything from the hand of one. If a woman has to give anything to a monk, she first hands it to a man, who then presents it.

-Social Norms : Thais don't 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.
-Thais regard the head as the highest part of the body, literally and figuratively. Therefore, avoid touching people on the head and try not to point your feet at people or an object. It is considered very rude.
-Shoes should be removed when entering a private Thai home.
-Public displays of affection between men and women are frowned upon.
-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.
-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.
-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. Unfortunately, this fact is known in some of the more tourist areas and you must try not to loose your temper if you are being scammed or ripped off. Stick your ground, DO NOT start shouting but be firm and speak slowly and  clearly. If that fails, call the tourist police who will try to mediate the situation.

-Drugs : Do not take drugs whilst in Thailand, this could land you in serious trouble even for small amounts.
Penalties for drugs in Thailand are severe and Thai prisons are notoriously poor. Corruption is a problem in Thailand. Avoid drugs at all costs, anyone offering to sell you drugs whilst in Thailand is more than likely an attempt at extortion.
"Possession of Marijuana can lead to a prison sentence of up to 15 years plus a fine of Baht 150,000 (£2,300). Amphetamines and Ecstasy are regarded as a class A drugs and possession or trafficking of them carries the same penalties as, for example, heroin. Possession of 20 grams, or over, of a class A drug at a point of exit from Thailand results in a charge of illegal possession, possession for distribution and attempt to smuggle and export, i.e. trafficking. A guilty verdict usually attracts the death sentence.
There have been a number of incidents where tourists have had their drinks drugged (in both tourist areas and red light districts) by prostitutes/transsexuals ("lady boys"). You should be careful about taking drinks from strangers and be wary at parties, particularly the Full Moon party on Phangan Island"- Source : British Embassy Bangkok Travel Advice

Beware

 •Taxis- Avoid unmarked taxis and maybe tuk-tuks. Official taxis are safe, have aircon and are metered so you avoid mad tuk-tuk driving, air pollution and money squabbles - and will probably pay less for the trip anyway.
• Jewelry- Never buy jewelry or gems stones from sources you are unsure about. There is a very old scam where you will be approached by a smooth talking 'businessman' who claims to trade in gem stones abroad. They usually hang around at popular tourist spots looking for victims. The hook is that they are in the country  to take advantage of a government 'tax free export' period that is soon to expire. You will be taken to what looks like a fully legitimate jewelers that is there one day and gone the next. Victims part with thousands on their credit cards to leave with a pile of papers and receipts promising the shipping of the gems to their home address which of course never arrives.

If Something Sounds Too Good To Be True, It Usually Is Too Good To Be True

• Intimidation - is a common tactic where a customer has been taken to a "private" shop back inside a soi. If you do not have the experience to deal with these situations, avoid them entirely. Simply get out of the taxi or tuk-tuk and walk away. If you are followed or threatened, find the nearest police box.
• Tour guides - should not be taken on a shopping trip. They will likely be making a commission of 10 - 20%

Atms and Credit Cards-
Thailand- particularly Bangkok- has some of the highest rates of credit card fraud in the world.
Skimming- The illegal copying (stealing) of the magnetic stripe data of a genuine card, including the encryption value, and subsequently transferring the data onto a counterfeit magnetic stripe for illegal usage." Skimming involved the solicitation of merchants' owner and/or staff by the counterfeiting groups in stealing of the magnetic stripe data from a customer. Most of these merchants identified for skimming activity are those that process the credit card 'out-of-sight' of the cardholder, i.e. restaurants, nightclubs, pubs, discotheques and hotel front offices, etc. Most of the credit cards data are skimmed using these devices. Please take note that a skimmer on average is only 10 cm in length and can be easily concealed from view. To avoid detection, the perpetrators have also cleverly disguised these skimmers as a Y2K checker and pager
ATMs- Ensure no one can see your credit card code number when you key it into an ATM [bank cash machine], or you may find a bogeyman has memorised it and will later steal your card and buy himself some new toys with it.
- If your card doesn't reappear from the ATM, check that there isn't a tiny foil loop blocking its exit - a device known as the Lebanese loop that allows the thief to retrieve your card later.
The latest scam involves thieves putting a thin, clear, rigid plastic sleeve into the ATM card slot. When you insert your card, the machine can't read the strip, so it keeps asking you to re-enter your PIN number.
Meanwhile, someone behind you watches as you tap in your number. Eventually you give up, thinking the machine has swallowed your card and you walk away. The thieves then remove the plastic sleeve complete with card, and empty your account.
The way to avoid this is to run your finger along the card slot before you put your card in. The sleeve has a couple of tiny prongs that the thieves need to get the sleeve out of the slot, and you'll be able to feel them.