My MIL is toxic. I say that, not because I don't get on with her, but because nobody gets on with her. She does not like anyone and nobody likes her - which is really, really sad.
She is the most difficult and unloveable person I have ever encountered, I find her impossible to comprehend or understand. She cannot be bothered with anyone, including her own children and grandchildren. She is entirely self centred.
She dislikes any closeness and intimacy.
She does not seem to feel things the same as other people, so she is never able to respond to people with any empathy or kindness.
She will never admit to being wrong or apologise.
She does not know when to shut the fuck up.
What has made her like this?
We are certain she is on the spectrum (not just my opinion, my DH works in this field & my SIL has a child on the spectrum). This, of course, would never have been picked up and addressed in her childhood, so she has received no help for this.
We are also certain she has an eating disorder, she is so skinny and obsessed with people's weight - it is the primary way she judges people.
She has a massive inferiority complex and uses her weight and her wealth to make herself feel better than other people, as she thinks everyone is judging her. Probably because she judges everyone.
Sadly, comprehending some of the reasons a toxic person is toxic, does not make them any less toxic.