https://www.believemypain.com/
Years ago I posted a study on here that came to the “same” conclusion. Which is, when asked, black people believe they don’t receive equal pain management, despite no medical difference in diagnosis. The absurdity is unreal.
TBH I really can't flesh it out more. It's simply a dark humor healthcare meme.
It's through experience.
I would say it's mostly women that declare this to you in practice.
But someone who authoritatively declares "I have a high pain threshold" will inevitably down the road be one of those "I know my body types" who wouldn't listen to reason and inevitably will be demanding opioids and inappropriate treatments down the road.
Edit: r/medicine are all insufferable COVIDian traitors to the profession, but here's an old thread discussing the phenomenon
Edit2: Giving it a little more thought, I think it's patients self-identifying as "terminally unique". "I'm not like the other girls, doc". It's a disclosure that they have an inflated sense of self and hence expectations that they are better than the average bear.
Few people with actual high pain tolerance will word it like that, they'll word it like "just get it fucking done, I'll live.", because a side effect of developing a high pain tolerance is realizing just how much pain one can be in... And usually not wanting to test that limit further.
As for "it's mostly women", plenty of scientific studies on that; women have much lower pain tolerance levels than men for both sustained over time and intensity. If they didn't produce a shitton of very strong stuff naturally in their body in childbirth, the human species wouldn't've made it, but that's not their normal mental state: A male crackhead can also take quite a bit of pain at the peak of his high.