Sorry arsenal, but on this occasion, I disagree with part of your post. And I agree with the comments made by colmx at posts #6 & #7.
When I first moved to Hua Hin, I got to know a crowd of fa-ràng expats and was introduced to a few hi-so Thais. I was told that when meeting the Hi-so Thais I should initiate the wâai on each occasion I met them for the first time.
I was also told that I should not initiate or return a wâai to restaurant waiting staff, hotel staff or shop workers. A simple nod of the head or a smile would be sufficient. I think it goes without saying that westerners should not wâai prostitutes or other westerners.
There was however one exception, and that was a very grand fa-ràng lady in Hua Hin who had indeed ‘gone native’. I was told that I should also initiate the wâai when greeting her. On the few odd occasions that I forgot to wâai her, crikey! I received the most icy cold stare and received curt ‘yes’ and ‘no’ answers for the rest of the evening, i.e. if she even deigned to talk to me at all. Cripes! Such severe punishment for what should have been a trivial thing of no consequence to her.
And on the first occasion I went up to Chaiyaphum to meet my first Thai boyfriend’s mother, father and other family members, I was told by my boyfriend and his Thai friend that I should initiate the wâai when greeting his mother, father, aunts and uncles. Oh, and any of the great and the good of the village who came to gawk at me (well, they didn’t exactly say ‘gawk’, I made that part up ).
In short, I would contend that there are indeed times when fa-ràng should greet Thais with a wâai, but unless you know of any grand fa-ràng ladies who have gone native, then I recommend you don’t wâai other westerners. But whether you think it is suitable to greet fellow westerners with a high-five, a clashing of knuckles, or a kiss on both cheeks, well, that is entirely up to you.