Sorry, didn’t read all comments, but what comes to mind:
• handle cash carefully, notes wrinkle-free, offer king’s head upwards toward receiver
• never throw anything, even a ball or keys..
•never drop anything, not money, not keys, nothing, always offer things with open palms upwards for others to pick from there..
• don’t try to force eye-contact, while Thais will make eye-contact, you are not to force eye-contact, especially toward same sex.. it is nothing to do with anything sexual, it is merely rude.
• Thai’s will not appreciate your try of speaking Thai to monks, Thais speak a different language to monks and to royalty, rather let someone interpret if you are to be respectful of their beliefs.
• Many Thais are unlikely to think in terms of disappointment with expectations as they culturally, if not religiously, think things as karma/kamma and as they are.. So they might not be cursing the missed train..
•as unlikely as it is in a western country for someone unknown to smile, as likely it is in Thailand for someone to actually do so. If a tuk-tuk driver from Isaan is bullying you for a ride in BKK, he will not stop with words or anger, but if you smile at him, he will immediately realize that you won’t be going for his ride and smile back at you.
•treat pictures of anyone as you would treat someone’s head..
• Try not to insist on things expected in your culture. 99% of the case the Thai person has not visited your country of origin or thought it necessary to understand it’s customs. It is his/her country more than yours.
• don’t be the tourist to load his water-gun with ice or piss during songkran. If you are not a clueless first timer to the festival you probably want to be visiting Cambodia at that week.
•Having visited every island, Hua Hin and Pattaya, you have not yet managed to visit Thailand at all.
• Thais are more likely to report your use of drugs than tolerate it. Prison is not a nice place there, and the guards are more likely to see your inprisonment as karma than with understanding.
• If you don’t know what is wrong, smile, bow and look clueless. This will shut up anyone yelling at you.
• You are most likely pronouncing every word of Thai in one of the other 4 possible wrong tones. It is as inconceivable for a Thai to try to guess the word you meant from the words /nāː/nàː/nâː/náː/nǎː/ in Thai as to guess the English word “presidency” if someone said “lollipop”.