When it's my turn to clean the bathroom, I'm going to use my stepmom's toothbrush to scrub the toilet.
She's still a family member! Why would you do such a thing?
I really don't like my step mother very much.
Just because you dislike her, doesn't mean you can do terrible things to her. It sounds like you already know this is a bad thing to do and you shouldn't do bad things to other people.
Stfu bitch don't tell me what to do.
I think you need to try and calm down a bit before thinking about this again. How would your dad feel that you aren't treating your step mom properly? I think it would be more worth it to try and voice your problems with them, and work them out slowly instead of making her life hard.