I'm 20 and she's 22. She's been diagnosed with Bipolar disorder and has been hospitalized for a month or so twice. Living with her is unbearable. She is unreasonable and truly a terror to be around. She is violent and unpredictable. She routinely berates my parents (calls my dad, who had suffered a severe stroke, a worthless retard [his speech was affected] and she wishes he died instead) and is extremely hostile to me about everything. I think she's jealous that I'm making something of myself (I'm going to law school next year) while she's probably going to be a drain on society for the rest of her life. Also, she decided to stop taking her medication recently and is noticeably more horrible to be around.
An example of her behavior is that just now (minutes before I am posting this) I was watching TV with my mother downstairs when my sister came up and shut off the TV and walked away. Literally no reason at all - she walked down the stairs wordlessly, shut off the television, and went back upstairs. My mother protested faintly, "Honey...why would you do that?" I got up and turned the TV back on, and my sister came back and shut it off and unplugged the cable box and walked away. I said something to the effect of, "Are you ----ing insane? Why would you do that?" So I went back and turned it on and plugged it in. My sister came back a minute later, walking toward the TV, and I stood in front of it (I am ~180 lbs and squarely built). I told her clearly to "---- off, I'm watching TV now," and turned my back to her to watch it. She punched me in the back of the head (in front of my mom) and when I whirled around, she was in a stance like she was going to fight with me (I wasn't scared or hurt, really, it was more of a, seriously? Really?). I was like, to my mother, "Are you going to let her do that?" Apparently so. So I went up to my room to write this and I am livid. This is the kind of thing she does on a regular basis. I could write about twenty similar stories from this past year alone.
Anyway, the worst part is that my parents do nothing. Absolutely nothing. They hope that she will get better on her own, and that she will "grow out of it." The thing is, they reinforce her insane behavior by allowing it to go on. I've spoken with my parents about it, even in front of my sister; lately, my go-to line when she is acting insane is to say, "She does not belong around people. You should kick her out of this home." My dad says that he just "can't do it. He has two children and he can't kick one out. What if it was me that had the disorder?" I agreed that while family is important, she is making life horrible for all of us, and there should at least be the stipulation, "act like a human being and you can continue to live here," but he said he would under no circumstances make her leave. Exasperated, I've asked my dad whether he could at least punish her, but he says punishments don't work on her, whatever that means. They give her an allowance, so I suggested he dock her allowance when she acts like a monster, but my dad refused the idea.
I hope this doesn't come off as an incoherent rant - there was no revision process and I threw a lot of information in, so I'll just sum up what I'm hoping for here: I would like information on whether acquiescing to insane, irrational behavior will likely result in bettering or worsening of her behavior. My parents think it will make it better, but I hypothesize it will make it worse. I am not an expert in mental illness (in fact, I know nothing about it), so I was hoping someone could let me know. It would really mean a lot to me.
Thank you.