When I met someone with bpd, I decided that I didn't want to be friends with them just because of that.
Why wouldn't you want to be friends with someone like that?
Badly behaved people, you never know what will happen.
Well, that's your choice!  People should be free to pursue friendships with whomever they want.  Nobody says you have to like everyone!
She's evil and she will hurt me one day.
You can keep your reasons to yourself, because if you're not their friend yet and don't want to explore that option then it is your right. You don't need to be friends with someone that you don't get along with.