Beach volleyball story, sort of: A year or two ago, I got Misty May-Traenor personally annoyed with me.
My niece was in the same gymnastics class as her daughter and they were good friends.
My niece is an absolute psycho, and her highest goal in life at the time was to learn more dirty words and rude gestures. She knew such words existed, but the adults in her life had mostly managed to keep her from learning them. She had "crap" and knew that there was an F word but didn't know what it was. With me being the fun uncle, she had identified me as her best shot and frequently begged me to teach her new swears and gestures.
So remember that bit in Talladega Nights where Ricky Bobby gives his rival an upside-down middle finger and says "Can you hear this? I better turn it up" as he rotates his hand up? I taught her that but with the 90s forehead L instead of the middle finger. Within a week, all the girls in the gymnastics class were doing it, and a three-time Olympic gold medalist was among the gym moms annoyed with me for introducing it.
Bonus psycho niece story:
I took her and two of her younger siblings to watch some friends play beer league hockey a few years ago. We sat behind my friends' bench and I taught the kids the concept of heckling, giving them some cleaned up lines from Letterkenny to yell at players from behind the bench. It was all in good fun but I got a little carried away and had my 7 year old niece yell "that was your guy 2-6, just end it you bender" and her younger sister chimed in "yeah just end it."
I immediately realize I had gone too far. But you can't just tell these kids "I shouldn't have taught you that, please don't repeat it" because that just tells them they have something good and they'll never let it go. So I told them that "bender" was a super naughty word, like the worst word ever, and I shouldn't have taught them that please don't repeat it. They were so excited to know a super bad word and whispering it among themselves that they forgot the rest of the stuff they learned that night.
Six months later my niece is in one of her oppositional defiance fits and screams "I hate you, you *bender*" at her mom and waits for the big reaction she expected for using such a horrible swear.