I'm caring for my elderly parent and I'm starting to hate him.
What is making you hate your father?
He yells at me and seems ungrateful that I'm helping him.
It's wonderful that you're helping your elderly parent but you have to be more patient with them. They may not understand that they are annoying you with their behaviors. Try to be patient and kind with them.
I can't take it anymore. They deserve to rot alone in their own shit.
Elderly parents can be frustrating, especially when they seem ungrateful. No one deserves to "rot alone in their own shit" though; please try to be patient and kind to him.