I too, have a mean mother. She is reformed... slightly.... for now. We shall see.
I had the typical immigrant's child homelife: EVERY test had to be perfect. 98% on a test? Where was the other 2%?? Nothing was ever good enough. That was the nice stuff.
The bad stuff: constant unending criticism about my weight (too fat), and my clothes (made me look fat). Constantly getting slapped (that lasted until I finally hit back at the age of 15). Constant complaints about how awful my father was (they were separated at the time). Indifferent contempt toward gestures of affection. Rude behaviour to service people and strangers. Obsessive about money and paranoid about it.
She got really crazy after I went off to university. Because she wasn't in the same province anymore, she appointed a family acquaintance whom I barely knew to be a "surrogate mother" to me. She would INSIST on my going to this woman's house to give presents on birthdays and holidays , she would INSIST on this woman being included on the rare mother-daughter visits she made to see me. And every single time, my mother would blow an absolute TANTRUM because I didn't treat her friend right. She would claim that I was rude to her friend and get mad that I didn't treat her friend like .... a mother!!

Bizarre, crazy behaviour. My poor DH even got to see some of it. It's a miracle he still wanted to marry me.
My DM basically made my life such a living misery that all I ever thought about was leaving home as quickly as possible and staying away.
She tried some of her crazy behaviour when DD was born, but my foot came down HARD. I told her off (and the blowup was absolutely monumental!) in no uncertain terms and wound up cutting off contact for almost an entire year. She's slowly earned back the privilege of regular contact, but it's probation for life. My mother KNOWS that I will cut her dead without a second thought if she looks cross-eyed at my family even once. I think that's the only thing that makes her stay in line.
Even now, DH and I can tell if my mother is in a "mood", but I just get very cool, refuse to engage, and cut the visit off immediately. It's her problem and I refuse to make it mine.
Sorry for the long post, obviously this has struck a nerve!!! To the OP - be strong, you have my complete sympathy.