Could that be a rare case? I am 100% Thai and have always received good to excellent ground and in-flight service. My last visit to the Royal Silk lounge was very good, the hostess Sawaseee Krap/Kha to me and helped me find a free seat. I frequent on the LHR route in Royal Silk and as one of the few Thai people in the cabin, the FAs always spoil me with surprises such glasses of Dom Perignon and First Class amenity kits etc.
You should write to TG about the unsatisfactory service you experienced at BKK.