Well, it depends.
Worst, physically, was when my mother would get into one of her crazy moods and start beating the crap out of us - slapping, hitting, hair pulling, etc. Not real fun.
Worst, mentally, was when she would walk away to think about it, then call you back and make you listen, and listen, and listen, and listen. I'd almost rather be hit.
Worst, chore-wise, was when she would go crazy and pull everything from our closet, dressers, shelves, backpacks emptied, books off of bookcase, etc and throw it all in the middle of the floor and tell us that we can't come out of our room until it was cleaned. Ok, whatever, except I shared a room with 2 sisters and the amount of "stuff" that was pulled was enough for about 3 days of cleanup. And eventually, there was usually a belt involved at some point.
Worst, anticipation-wise, was on Sundays in the car after church - the dreaded words "when we get home, we are ALL going to clean the house" because that was prime time for mother to go apebat-crazy and start her screaming, yelling, lectures, hairbrush-wielding, belt-hitting psycho-ness because the kitchen floor didn't get cleaned "correctly"
On lighter notes:
1. When my sisters and I fought, having to stand in front of our mother and say we are sorry to each other, then have to hug each other. LOL
2. Having to do dishes after dinner in 100 degree summer weather and singing church songs at the top of our lungs
3. Being grounded to our rooms for the afternoon and forgotten about, but getting out of being called to change laundry loads or fetch something for our mother.