one time I tried telling a TERF about Swyer syndrome, aka XY gonadal dysgenesis. It's a intersex condition where the individual will have XY chromosomes and often intersex genitals, but it also presents itself in female seeming people with otherwise typical genitalia who might be unaware they have a condition. There has been at least one incident of a person with Swyer syndrome giving birth through a specially designed fertility program, despite being born with XY chromosomes.

After telling this to the TERF in question she responded. "Yeah but they aren't supposed to be born that way."

yeah ok and 1 in 100,000 people are born that way, guess they shouldn't exist.

i imagine at least 1 terf was so paranoid they had themselves tested