I disappointed my mother by being born at all. She hadn't wanted a second child.
By being born female - "If I had to have another child at all, I wanted a boy. I don't like girls." She was always asking me why I couldn't be more like my brother, instead of being "peCULiar" (that's how she said it).
By being a poor replacement for my dead sister, born two years before me (she only lived a couple of hours after birth). When I found out about her, I was thirteen. I found her death certificate in a drawer. When I cried for my unknown sister, mum sneered "I don't know what you are crying about. If she'd lived you wouldn't be here."
For being too like my father. She hated him, and she hated me. She thrived on chaos and uproar, and beat me because she enjoyed beating and I was too small to hit back.
For not giving a fuck about a clean house (still don't).
For not wanting to give her grandchildren to boast about. (I was married to the wrong man and had grave doubts about my ability as a mother. Also it turned out I have bipolar disorder. I think my decision was right.)
Even on her death bed she could squeeze out a word or two for the nurses, and a word or three for my brother. All I ever got was "Grrrrrrr". I was the one who'd propped her up, run around, listened to her whinging about everyone.......
I loved my dad but he disappointed me by not stopping my mother's abuse.