Here's a shitty, not-fun one.
When I was a kid in daycare, I used to pick on this one kid. It hadn't even occurred to me at the time, but looking back now, I realize he was mentally handicapped. My bullying wasn't even about him being handicapped, I don't think I was even aware of what that meant. I just decided in my shithead mind that he was stupid and I didn't like him, so I hit him a lot and called him stupid.
I was like six years old at the time, so I mostly chalk it up to just being an asshole kid, but that isn't an excuse. I was a dick. I still feel kinda bad about it sometimes. I wish I could find him now and apologize, because I really was a bully to him. I was a piece of shit for a lot of my childhood.