This is what teaching in Thailand means in most places but not everywhere. I've been teaching here for almost 18 years and I've seen enough to write a novel. In my early days I used to keep quiet and bear the unbearable most of the times.
Now, I reached the point where I simply show them the middle finger if I have to.
I understand Thai and if they try talking bs about me I fight back on the spot. I'm fully qualified and have the Thai teaching license, so finding another place to teach isn't a big issue.
They tend to behave like this especially with young, newly qualified or underqualified teachers (no judgement here, no one was born fully qualified) or with those who struggle to find a job because of their nationality or color (yea, Thais are extremely racists).
In the end, what doesn't kill you makes you stronger. Time to move on.