My brother and I were raised by our grandparents and turned out very normal I guess. My parents raised my sister and they had very different conflicting parenting styles (they are now divorced which seemed to stem from my sister's problems) which essentially resulted in her never getting diciplined for anything ever. The results have been a 7th grader who has about 2 full blown temper tantrums per day, bullies her peers, ignores (literially pretends she doesn't hear) anything she disagrees with, is completely self centered and doesn't try to hide it, and is very materialistic. No one in my family wants to be around her, even my parents. 

Some examples of her behavior: she tried to stab me twice growing up, my brother once, and my mom once. She kicks my cat to get to me. She will ask my mom to buy her things everywhere she goes and when my mom says no she will have full blown tempertantrums in the middle of the store. She says that she hates everyone behind their back (my dad's girlfriend, my mom, my boyfriend, my brother) just for attention. She looks under the tree at christmas and sees that she has one less present than the rest of us and then throws a fit because of it, etc. My mom started drinking heavily at least in part because of her, and my dad was borderline emotionally abusive to me to take out his frustration for over three years. 

Today we celebrated christmas at my mom's house, and a large chunk was tainted because of her behavior. My boyfriend, brother, and I are all back home from school for the break and wanted to spend time with my mom but she turned it very negative. It's my mom's first christmas after a divorce and she has no one to spend it with, and my sister didn't even care about how selfish she was being. Once we got home I was sitting on the couch with my boyfriend being sad because of how it turned out, and my dad saw me and wanted to get me to talk about it. We talked for a second, just mentioned that my sister was rough today and it kinda sucked. What he said boiled down to "she just wants to be included and I know it's hard to include her but it's important to understand" which is true, (I'm not trying to call my dad out for this) that is the reason for her outbursts, but at the same time when she has such bad behavioral issues it feels impossible to be around her at all. This is an assholeish thing to say but honestly I wish I wasn't related to her at all. 

I guess the core "am I the asshole" is I am away at college all year, and I have the option to spend breaks with my boyfriend's family. I love my family (excluding my sister), but every time I come back I feel awful because I truly can't stand to be around her. I don't want to talk to her. I don't want to text her back when she texts (and I haven't been), I don't want to try to be friendly, I don't want to be the "good big sister" anymore. I tried that for years and all it got me was anxiety, abuse, and loss of friendships from people not wanting to be around her. I don't want to be her sister at all. Don't want her to visit me, don't want her to come to my graduation, don't want her to be in my wedding if I get married, don't want her to be around my kids if I have them. I want to tell my parents that I am distancing myself because of her, but my dad has always said that family has to come first, and he stopped talking to his own mother for a while because she didn't invite my sister to a family dinner. My plan is a bit more serious. I would only visit for short periods of time and stay where she isn't. I would also not communicate in answers more than "yes and no" with her unless it would disrupt someone else in my family. AITA for trying to get away?