I'll give you a specific story to talk about what I mean.
I had been teaching under him for 4 years at this point. I was a 3rd degree black belt. I was there for every class; 5 hours a day, 6 days a week (on top of my day job). My typical routine was that I help out with 4 classes and take the 5th. I wouldn't take any break during the 4 classes I was helping with, then I would take a quick break during the black belt class stretching and warmup to use the restroom and get some water. Usually I would get back at the end of stretches or the start of punches. My rationale was that I didn't want to waste his time and money (when he's paying me to be an instructor), but it was okay to waste a little bit of my time and money between classes. (Classes were back-to-back with no break, so the previous class ended at 7:50 and my class started at 7:50).
One night, a student comes up to me at the end of the previous class to ask a question. She wanted to practice on a heavy bag at home, and wanted to know if it was a good idea. My opinion, which was informed by the opinion of another instructor at my dojang and also an overwhelming majority opinion online, is that this is a great idea to reinforce proper technique. I told her its a good idea. Then took my break. When I got out of the restroom, the Master had already started into the technique portion of class. I went to get on the mat, and he very sternly told me to wait.
Then, he went over some of the 3rd degree testing material that I needed. He hadn't gone over it with me yet in class. None of the students on the mat needed it. They were all 1st or 2nd degree. He specifically had them learn something I needed while I stood on the sidelines. Then he had me come on the mat, and the rest of class we only worked on 1st degree material.
After that, he called me into his office. He questioned my loyalty to him, because I skipped part of my class. He questioned my ethics and integrity. I tried to explain what I said above (about respecting his time and using my time for the break). He explained that all the other instructors were on time. (The other instructors had been there for only 1-2 hours, and were not leading the class as I was). I finally drew it out of him that he wanted me to take my breaks at the end of the previous class, instead of at the start of my class.
Then he asked me what the student had asked me about. He told me that I was wrong to tell her to practice on a heavy bag, because of his past experience where students have had injuries and needed surgery (no details about it). That if a student asks a question and he hasn't told me the answer, I need to refer them to him instead of answering on my own. This is what confirmed for me my suspicion - he wasn't actually mad about me being a little late to class. If he was, he would have spoken up 4 years ago. He was jealous that a student went to me instead of him.
For the next 2 days, at the end of every class I was in, he publicly and sternly told me to take a break. After those two days, he called me back into his office, and said, "Do you understand now or do I need to keep telling you?"
I think he treats his instructors as the release from the frustrations he bottles up from the other students. And he can't take his ego being challenged. This was one of the incidents that is why I was planning on quitting, because he would do stuff like this. He wasn't physically abusive, but he was emotionally abusive and manipulative.
