Hi,
I recently stumbled across this forum and hope it can help me solve a question regarding mental health.
My younger sister is currently 18 years old, and she is entering her last year of high school. I'm worried because she acts very immature for her age and believes that she is better than everyone else. It surprised me that she even admitted it to our mom: she claims that she hates her friends, hates everyone around her, and calls herself a "queen". She is also very sensitive and cannot take critisism at all, even if it's plain old advice—she explodes and fights with anyone who says anything about her, and she does it in a violent manner involving hitting and screaming. She also tends to talk about herself and her problems all the time, and pretends she doesn't when we (me and mom) point it out. One other thing I've noticed about her is the way she can easily insult someone, even if they've completed a task for her. For instance, about two weeks ago I let her borrow $80 and told her that she needs to pay me back whenever she can. Not only does she refuse to pay me back, but she even called me a "fat, greedy b****" when i mentioned it to her.
Being 22 years old, this kind of behavior is past me. I don't react or find it insulting, but i am very concerned for the people around her. I wonder if it's a mental disorder? Neither me, my mother, nor my two older sisters ever behaved this way at 18. I also wonder if my younger sister is perhaps mentally developing late? She's always stuck in the past as well and blames everything (including her outbursts) on our mother. I think it's narcissistic personality disorder? Correct me if I'm wrong! Thanks for your help!