I feel like I want to be estranged from my father and I think he deserves a slow death.
Can you explain to me why you are joking like this? Or are you? Why would you want that sort of death for your father?
It's just how I feel.
Not all family relationships are healthy and it can be a good thing to cut ties with those who are toxic. That said, wishing death on another person is not a good thing and the feeling is probably making you feel down.
I'm fine. I don't care if my father dies slow and painful.
While you are clearly going through something with your father, wishing him a slow and painful death would be considered taking things too far for most people. Have you ever considered trying to open a dialogue with him and allowing him back into your life? Giving family second chances can be a beautiful thing if it works out.