A particularly weird and disgusting one that I heard from far too many adults as a kid, was "pull your finger out of your arse". This apparently means 'get a move on' and/or 'stop being lazy'.

As a kid with autism it really grossed me out to think all the adults who said this had decided I was slow/lazy because they thought I was regularly putting my fingers in my bum.

Being an adult who has tried most sex stuff now (and also witnessed and spoken candidly with many others who have too), I can unequivocally state that anal play involving fingers, either with a partner or alone, does not correlate with difficulty completing tasks or laziness, either during the act or afterwards. And that the folk I've known who have admitted to trying this, are seemingly not any lazier or less efficient than the folk I've known who haven't.

I still don't know why or how "pull your finger out if your arse" became a phrase meaning what it does, I'm going to hazard a guess it's based on homophobic stereotypes, but even then why was it said to me as an afab child? Maybe it was supposed to be funny.