1. Thin- Other Asian cultures like Japan are thin and petite, but Japanese for example can be a little thicker in the waist and legs. Thai girls have perfect waist, hips, BUTT, etc...
2. The amazing Thai smile. I would have to attribute this to perfect bone structure in the face. I can always tell a SE Asian girl by the smile they have. Full wide toothy smile, with the average girls having a better smile than any actress in the US.
3. Face- Thai girls have narrow faces with high cheekbones. The most awesome look ever. Some other Asian cultures like China can have rounded faces. (not all, just a generalization)
4. Beautiful long silky black hair.
5. Sweet and sincere- Yes, this is not a physical quality, but to me it is maybe more important than all the rest. There are beautiful women all over, but I have never met such sincere and caring women as Thai. If the most beautiful woman in the world is cold, callous and cares only of herself, to me she is ugly.
I would say SE Asian girls have all the BEST qualities of Asian girls everywhere.
When I first arrived in BKK and went to Siam Square, I saw the most beautiful woman just standing drinking coke from a bag. (like a cup) I was actually shocked. Tall, long legs, beautiful hair, amazing face, and smile. What was more shocking was that those types were EVERYWHERE!!! It really took me weeks to get over the fact that Thai girls are just so amazingly beautiful.