CRON posted... You're correct. It's not like someone just develops a personality order and becomes abusive.
That said, based on my experiences, the experiences of others, the experiences of people in a support group I went to, and the experiences of others online... abusive, toxic, angry, manipulative behavior seems to be consistent with people who have BPD.
Again, at that support group, literally every single person raised their hands when the person who led it asked us if we were ever abused. Everyone shared their stories over the course of two meetings and everyone had almost identical stories of how they were manipulated and abused. When I was looking for support and advice online, every story I read felt like the same experiences I had.
"data" is not the plural of "anecdote"