I'm going to push my sister down the stairs
Why would you push her down the stairs?
She is always snooping around and I've had enough
You cannot justify harming someone just because they are doing something you do not like. I would recommend to talk to her or move out if she really keeps on snooping. If you push her, she may die and you may go to jail.
Damn. I feel like I'm going to regret this later.
I think you would definitely regret hurting her. Just try and have a conversation with her instead.