What reason to give to colleagues about why I'm leaving?

[Newstart9764826]

I enjoy my job and get on with everyone there, they are all lovely, apart from my direct line manager. This person seems to take pleasure from making people's lives hell. There have been complaints before and nothing done so no point me complaining.
I could tolerate this person better if there were more of us in the office but we work closely together every day and there's only a couple of us. It has come to a head now where my mental health and even physical health is being affected and I have made to decision to leave.
People will be surprised and I expect a lot of people to come and ask me directly why I am leaving. I dont have another job yet either so can't just say that.
The singular and only reason that I am leaving is because of my manager but I can't say that to people as I need a reference from work.
I have put the reason on my resignation as personal reasons but I will probably be asked to expand on that by higher ups and may even be asked to stay but I cannot. Nothing is worth how this person makes me feel and it is a low paid job.
I dont want to leave on bad terms.

Best one I heard was from a manager who said it was either leave now or she never would as she was so comfortable but needed to take a risk and jump.
Aka Caroline's a cunt but I can't say it as we're in a small area and I might end up working with her again in the future.

This was me several years ago. I got signed off and resigned with no job to go to. I put on my resignation letter that it was time to move on. My manager (who was toxic and the reason I left) told people I was retiring (I was 49!). Speaking to ex colleagues after I left, they said that they knew what she was like and particularly how she treated me. Some begged me to report her because, as I had resigned, I had nothing to lose. I wish now that I had told someone higher up the real reason but I was not in the right place mentally at the time to do that - I just knew that I needed to get out. Since I left, there has been a mass exodus of staff - all because of one toxic person.

Is there an HR? I'd be asking what type of reference the business does. Lots of places don't allow managers to do references, it's just a factual one from HR with your job title and when you were employed.

Say you're moving house??

I would just tell the truth. You have nothing to lose.