Hmmmm. I've had a lot of shit in my life, most of it brought upon myself by myself, but I think the actual "worst" thing that I've experienced was having an abusive babysitter when I was little.
It felt like some sort of boot camp every day, my sister and I went there from the ages of like... I don't know... 5-8 or something? That may be totally off, I don't really remember. Anyway, the woman, Cindi, was just basically abusive in many ways. Each morning we would have to sit in the living room and play with toys, if we even GLANCED at the television and she caught us, she'd scream at us or send us to "take a nap" which was just punishment, and we'd have to skip lunch. Whenever it was TV time in the living room, we'd have to sit very still and watch TV, without looking away from it or falling asleep. Nap time was probably the most nerve-wracking for me, ever since I had selected the wrong bed to sleep in, and so Cindi came over, picked me up, and chucked me across the room so that I landed in the CORRECT bed.
What probably irked me the most was that Cindi was like, adamant that all kids had to play with one another. My sister and I were very close, and still are, and so we would always like, bring games for ourselves and play with ourselves, but there was this little bitch Meagan who would sit there and pout, and wait for Cindi to walk past to complain, and then we'd be forced to play with her. I think the worst thing I saw while I was there was this little boy, he was maybe 5 or so, sitting by the screen door in the living room that led to the backyard, and he was saying that it wasn't raining outside, although it was, and he and Cindi kept going back and forth about it until she finally opened the door, grabbed him like a sack of potatos, and threw him outside. "THERE, IT'S RAINING." He cried, etc, and I felt so terrible, I felt like I couldn't tell anyone how horrible she was because no one would believe me. Oh, and if it was hot outside she would make you play outside, and you couldn't come in to drink water or anything although we'd be out there for hours at a time. I don't miss that at allll.