It could be burn out, or it could be that you simply can't put up with their shit.
When I am burning out, I hate EVERY ONE. Every client passes me off, even the ones I usually like. And I'll internally lose my sshit over very small things.
However, I also know that regulars get very boring to me, unless we're doing something fresh on each session. Regulars also get comfortable after a while and feel they can act in ways they wouldn't if they were a new client.
I have cut regulars off many times, and I also feel better for it. I used to be in the boat of "awww they're not that bad, they don't do anything major" but it was more how I was left feeling after it that was the indicator that I had to let them go as opposed to what they had done.
Your body, your business. Don't for a second feel bad about what you choose to do in your business.