I quit a long standing run after 2.5 years where the control-freak producer/playwright/theatre owner kept taking away my responsibility and was just a growing nightmare to work with. I could not give the cast notes, or even tell them, "quiet backstage." I was allowed to make 15-10-5 minute calls only at his discretion. I was not allowed in touch-up, walk-on or understudy rehearsals, and was expected to maintain the poorly constructed set with no tools other than tape and not allowed to provide input as to how it could be repaired in a more permanent way. I really do believe he was a mental case who needed to be evaluated and medicated. I was told that he took all his clothes off during a rehearsal for his next show and tried to make the (all female cast) take their off, too because "everyone in it needed to be as comfortable with their bodies as he was with his."
I started contemplating quitting when he told me I was no longer allowed to make shopping lists of backstage supplies (toilet paper, spray starch, light bulbs for dressing areas and bathrooms, and the like) because I put down that we needed to buy more toilet paper when we still had two whole rolls left. Not packs, rolls.
I finally gave my two weeks notice (conveniently, two weeks before winter holiday break, giving them a full five weeks to find a replacement) when he came into my booth during the show and asked me to leave the show and go do a craft project for him. I said no. I think this may be the first time someone had said "no" to him in years. He threw what can only be described as a hissy fit, backstage, the whole rest of the show. We had a post-show talk that I doubt went the way he expected. I refused to give ground, and at one point, he actually stepped up onto the stage in an obvious ploy to use his height to intimidate me. Which did not work. Please, I've been short my whole life.
I explained to him what a stage manager was, what my professional standards are, and that if he was pissed at me to never ever EVER again take it out on the cast during a show. He tried to tell me that he owned me (no seriously, owned me like a slave with a time limit) during work hours and I had to do anything he told me too, and he was being courteous by asking. I then told him this was my two weeks notice, he was lucky to be getting that, and he could hire himself the personal assistant he wanted, who could also run sound and light boards, while he was doing his Christmas shopping.
The only thing I've ever regretted is not getting out of that toxic environment before things got that bad.