Wind your neck in.
I have no idea what this means (I mean I get it via context but no idea what it means from a “how it became a saying” standpoint) but I love it and I will be using it at every opportunity from now on.
I think it as an alternative (or derived) from ‘keep your nose out of other people’s business’ - though if so it has a different meaning now.
Also could be something derived from conflicts - ‘put your head down’ or ‘keep your head down’ etc - again a different meaning now though.