Well, my 12-year old sister hates me for literally no reason at all, and is actually proud to say so. She absolutely cannot spend a day around me without verbally abusing me. She can't go two days without wishing me dead. She steals and destroys my property. She deliberately arranges situations where I have to do things for her because no one else is available, and then goes on at length about how she doesn't care about what I've just done for her. She threatens my life. She physically attacks me in serious fashion - the worst was when we were in the car together, traveling at 65 MPH, and I was the driver. She's actually enraged me into what most courts would see as child abuse on two different occasions. I once seriously considered killing her - and it's all just manipulation on her part. If a shrink knew half of her history, he'd diagnose Conduct Disorder (or even psychopathy) in a heartbeat. I'd have to be the world's biggest, most gullible, most self-destructive idiot to tell her anything.
The worst part is, my parents - especially my mother - get the same treatment to a somewhat lesser degree, and they KNOW and AGREE on how bad she can be. My mother - who doesn't believe in hitting children for any reason - is deathly afraid to administer any kind of punishment or enforcement of punishment, even to drag her to her room, for fear that she'd lose control and wind up killing her through escalation and bottled-up frustration. Yet, nothing is done about the situation.
Maybe because of having to live through that sort of abuse together, I've got a close bond with my younger brother. I've considered telling him, but I'm just not sure how he'd take it, and I'd hate to ruin my relationship with him.