Normal behavior in Thai society is calm and friendship. In case of any dispute keep calm and smile. Never raise your voice to Thais. First of all it’s certainly impolite. Secondly you should remember that Thai language is tonal language. It means that as soon as you start to raise your voice, most Thais won’t understand what you’re saying.
It’s impolite to stroke Thai people heads or touch it any other way.
Riding motorbike (walking down the streets, visiting shopping malls, etc.) in batches or just without shirt makes Thai people confused. Of course they won’t show that, but this is going to be totally shocking for them.
Do not shout while walking the streets. It would enthrall Thai people quite much. They probably don’t know that somebody can yell so loud.
Drinking beer from a bottle, while walking is not very correct motion for Thai understanding. Thai thinking different way: if you want beer, just sit, relax and drink it. Why should you do that, if you are in hurry?
Nudism in Thailand is quite dangerous stuff. If you don’t want any problems with police – don’t flaunt you bodies. If you want to take a sunbath naked – visit small nearby islands. You probably will be only person there.
Perhaps the most basic: nobody owes you anything in this country. Don’t act bully and keep representing yourself as polite and well behaved man. It will do favor not only for you but reputation of your country also.