This thread is making me cry. I actually identify a lot with OP's mom, because I also have trouble taking criticism. I don't do the sulky, silent treatment thing when someone criticizes me, and I've only played the "Why are you being so meeeean?" card on a few occasions when under the "affluence of incohol."
But I was raised by parents -- mom in particular -- who couched every criticism and reprimand in "You're bad/unworthy/undeserving" language. It wasn't "You did/are doing something wrong." It was "You ARE something wrong." Delivered with anger or coldness that was terrifying, because it felt like emotional abandonment.
I'm in my 50s now and I know in my head that when someone who loves me takes issue with something I've said or done, it doesn't mean s/he hates me. But my childhood conditioning (criticism = withdrawal of love) still causes me to panic and become desperate for reassurance that this person isn't going to abandon me.
I think this is what OP's mom is doing with her behavior -- it's a cry for help, for reassurance. Unfortunately, I don't know if there's any magic formula to stop it. Refusing to deal with her when she's in her "you hate me, you big meanie" mode just reinforces her belief that she's unworthy -- it feels like the withdrawal-of-love thing. Even "Oh, Mom, stop it. You know I love you; I just don't like it when you do X" can feel like "I love you even though you don't deserve it, Interrupting, Grandma-Insulting Woman."
I wish I had better advice for you. But I hope my insight helps a little.
I am sorry you have struggled throughout your life with this - it must be awful to feel that way. As you said, though, you realize it is an inside job and not the fault of people around you. I wonder if showing this post (or something like it) to the mother might help her to recognize that while she feels what she feels, it really is not rational and not based in reality. The bolded language is especially clear for me - nothing anyone could say would change the mom's negative view *of herself.* It might help the mom to recognize that she is the one hurting herself by her behavior rather than other people ganging up on her.
Absolutely agree with TurtleDove here. baglady, you're not making other people pay for the unkindness with which you were treated. If this is the mechanism working on OP's mother, then she's letting her feelings run her thoughts and conclusions rather than questioning them and tending herself.
My mother received some appalling messages in her childhood. I am so, so sorry for her. But I am also weary and self-protective in the face of spending my entire life having moments of my healthy development and self-advocacy interpreted as a knife to her heart.
ETA: As far as etiquette goes, it was hard to find a solution when my mother kept reading rejection into what I said. Respectfully standing up for myself was seen as "you hate me." Agreeing to disagree was impossible -- disagreeing means "you hate me." The kindest solutions for me have been silence and bean dip. And here's where etiquette and rel@ationship issues overlap so beautifully: civility can sometimes make it possible to maintain a give-and-take with someone broken while treating everyone humanely.