Don't Be Unique
Western culture is inundated with a culture of individuality. Everyday we hear things like "be yourself" and "everyone is special." Everyone wants to stand out and get attention from his or her peers. We only conform enough just to fit in to our chosen click, and no more.
But Thai social culture is very different. The best way to fit in is to be just like everyone else. Besides, your peers are always watching and will gossip bad things if they find out you are different =P Be more humble around others, as the monks teach. Of course this just seems very strange to a westerner's perspective. Be like everyone else. Don't stand out, its rude. Jump off the cliff with everyone else!
This means you must join karaoke with them (gasp!) and do anything else the group decides to do. Saying you don't want to when everyone else does is just plain anti-social behavior.
Unfortunately as a westerner you will always stand out. Whether it be your western habits, the cultural mistakes you make, or just the color of your skin. Thais will always gossip more about you, always watch you more intently, and always think you are never one of them. But at least try with the below general rules, as they will get you far in making friends =)
Some General Rules
Suppose you are hanging out in a group of all Thai friends, you should always be a part of the conversation. Just nodding your head and smiling occasionally is considered rude. Say something every now and then, even if you are a quite type. Sounds easy, eh? But what if you don't speak Thai and that's the only language they are speaking? Yes, Thai's (who are fluent in English) have got mad at me because I didn't join an all Thai language conversation (before I spoke Thai). Annoying, no? There are two solutions. Interrupt with your clever English conversational material, or just walk away. Unlike in westerner culture, walking away from a conversation is much less rude than just smiling and nodding. One of those instances where your upbringing will cause a clash of the cultures . . .
You should also be aware of the type of people you are around. Different groups require you to be a different person. I have hung out with elite ultra-conservative Thais, as well as poor off the street Thais. They all have different standards. The less elite the Thai, the more westernized and accepting of you they will be. I actually enjoy being with the common Thais much more than the elite because they have much lower standards that I need to reach =P
Share! Thais like to share things more than westerners do. It's a great way to show social interconnectedness. If you are traveling with Thais, you will often notice everyone buying food and passing it around. I recommend you doing that too, even if you cant read the Thai packing labels or even recognize what the heck you are getting. After all, if you don't like it, someone could =P
Just remember, in Thai culture, the nail that sticks out gets hammered! Doing as the Roman's do will get you far . . .