Is it normal that I hate my gf's kid?

I feel the same about my BF's daughter. that's why I found this site. Looking for others who are basically good ppl but hate their step-kids
I don't know why - I also love the oldest of his girls but the youngest I can do wihthout - for no real reason. She's not bad. She is just annoying and my son hates her too
I love it when her father punishes her or yells at her - sadistic right?? God I feel awful
her sister has a hard time with her as well - but she's her bio sister, so, puts up with her.
this kid is the most annoying to me but for some reason - she's her grandparents' favorite
They always talk about her
she's fat, lazy, greedy - eats everything. I can't watch her eats it's disgusting
She's weird too- just stares at ppl. or if I'm doing something like making dinner - she just sits there breathing loudly from her nose and starts at me like I am doing a magic trick or something. I stopped answering her stupid questions : "where are you going" when I am walking around the house..geez!!
Sometimes, sheis following me around - all in my space and I'll slam the door in her face - and I feel good about it...I didn't think I can dislike a kid - 10 years old - that much