I too have a mean sibling, a sister.
She seems to enjoy hurting me, so I try my best to avoid her. When in the hospital for my depression, she doesn't try to hide her ridicule, calling me stupid, crazy, etc. I mean, she's always been that way with me while growing up, but now with my illness, she turns up the heat.
So what I'm doing now is not even calling her AT ALL! If my phone rings, I look first and have made up my mind that if I see her name on my caller ID, i won't answer. It's that simple. And if by chance I don't check, answer and find it's her, I'll just hang up that's all. I'm not trying to hurt her feelings, but then I'm not trying to get hurt again either!
How do I feel about that you may wonder? Well, while I don't feel completely happy about my decision, I feel good and at peace with it at the same time. My therapist talked to me about setting boundaries, and I feel that's what I'm doing.
There's no need to allow someone to continually put you down, and that includes even in your own family!
I'm 69 and I think I'm finally growing up! Lol.