My sister is insane and my parents don't believe me, what do I do?

BoyfriendMateriall
My sister is only 14, but she is a maniac. She regularly threatens to kill me with knives or blunt objects, and has a particular liking for threatening to "pop" my balls.

I have tried speaking to my parents about this but she always makes sure to do it when we are alone or out of earshot, so to them she is their perfect little girl and I must be exaggerating or making it up. This is despite the fact she has gotten into fistfights with other girls at school numerous times, and sent a senior to the emergency room with fractured testicles.

They seem hell bent on ignoring her behaviour, and I don't have any option of moving out any time soon. My only idea is to try to record one of her threats, but there's no way to tell when she'll do it and I don't really want to egg her on.

I would appreciate any advice.
My sister is insane and my parents don't believe me, what do I do?
11 Opinion