This blog is here for all Thailand newbies, welcome:)
The word is also spoken as a farewell as well.
Sà-wàt-dii is always added by polite particles to show respect to the adressee. The most common are ‘kráp‘, used by males, ‘kâ‘ used by females.
I got questions from my students many times that what they should do when being wai-ed to. You would be considered impolite if you didn’t return or at least acknowledge the wai. At the very least, you can smile and nod. Only monks and royalty do not need to return a wai.
It may look somewhat more awkward and funny when you do it, but the attempt will still be most appreciated and impressed. It might take you some time to perfect your technique, but please do not be shy to show your gesture and say hello just like Thais 🙂