Easy - their black and white attitudes on people flip so hard and often and they are very vocal about it so you'll notice this symptom almost immediately.
I think BPD is a disorder that has been written to only apply to a female phenotype, so that's why males rarely get diagnosed with it. Autism has been broadened to include other phenotypes, but BPD hasn't.
I've never seen a male exhibit BPD-like symptoms. It may be a case where they don't actively vocalize behaviors like black and white relationship thinking due to differences between male and female socialization.
Edit: Since we are off topic.
What a great temperament! Oh wait, it has no brain and cannot scream.
Also, I forgot whether it was true or not that Jaxon Buell
finally shed his moral coil. There was always fake articles about it almost like everyone wanted it to die.