In my case my sibling was actively encouraged and coerced by my mom.Mom used to encourage her to call me nasty names while she was very young and trying to learn speech. So at very young age she knew ,she could get away doing a lot of mischief. She used to spit on me and while I froze ,she used to smirk at me.She knew at a very tender age ,I have no one to turn to.She wrote graffiti in my books.I got in trouble in my school.The thing is I never knew it was her,until she told me recently and started laughing her b&tt off while I listened with bewilderment. I am not sure if she does it intentionally to retraumatize me.These are funny memories for her.Someone's trauma is a laughingstock to her.WOW,just wow.