I don't know any Khmer or Vietnamese but Thai's are some of the most aggressive people I have ever met in my life. Thailand wasn't colonized for a reason.
"I don't know any Khmer or Vietnamese but Thai's are some of the most aggressive people I have ever met in my life"
I hate to generalize this way but it seems true that the Vietnamese and Khmer are the nicest people around, unless and until you cross the line. The you're dealing with some really aggressive and volatile emotions.
Unfortunately the Khmer and Vietnamese have not been able to establish the kind of national unity seen in the Thais. I suspect that's because of monarchy, but that's just a theory.
Thailand was aligned with the Axis in WWII.