I've never been fired, but I once fired myself before I could be fired. I was a dean at my last place of employment. Everything was going great until we got a new provost (my immediate superior). The guy wanted me to redo a bunch of stuff I'd already done so he could take credit, and I refused to put my faculty through that. He also liked being kissed up to, and I'm not the kissing-up type. He also had a very bad habit of promising stuff and failing to deliver. Even with difficult bosses, there are many ways to accomplish what they want (or think they want), and I tried everything, but it was never good enough, and I was getting more and more ****ed off. I finally made a list of things he promised and, as each one fell by the wayside, I checked it off. When I got to the end of the list, I quit, because it was clear to me that one of us would have to go and it wasn't going to be him. I quit during winter break and he'd been out of contact; I sent the resignation straight to the president, who really liked me. The provost must have gotten an earful when he got back, because he had the gall to send an email wishing I'd told him first and can we work this out? I sent an email back saying, "I've been jumping up and down in front of you waving red flags for 6 months. Why should I think you'd pay any closer attention now?"
He was so bad the deans used to get together once a month for lunch and to support each other. He was so blatantly angling to be president at some university somewhere that he was kind of a joke. I experienced no small sense of schadenfreude when he finally got a president position and was fired a year later for violating some labor regulation in the state where he went. So far as I know he never got another position.
I'm not a quitter, but quitting that position was the best thing I ever did. I revived my geology research career and have been happy ever since.