There's only one reason that I post here and that's to annoy someone that I used to know.
Who's the person you're hoping to annoy?
Someone who hurt me deeply by badmouthing me.
Wanting to get back at someone for hurting you is normal but it's not something you should usually act on. Especially here because you said it was someone you used to know, you should have gotten over it by now. You're making things harder for them and yourself by still actively bothering them.
I can do what I want. I want to ruin this person's life and fuck their head up.
You can do whatever you want, that is completely true, but trying to get revenge is wrong. It's also just not worth it to attempt to annoy people, because you wouldn't like the same thing being done to you.