I've flown many times Thailand (BKK and CM) to Hanoi and Ho Chi Minh City to lecture at VN unis. Maybe 20 flights.
Seen plenty of Thai passengers being demanding.
Worst was a few years back. Thai lady said in English to the pleasant Viet Jet hostess "I will sit down if you can guarantee this aircraft is safe". Her Thai female companion then said "Do Viet Jet pilots have a pilots license".
They spoke loudly, no doubt looking for attention, many other Thai passengers booed them.
On all the VJ flights I've taken never once had any negative experiences, VJ staff always pleasant, polite and helpful.