I am so sorry, the first time I read it I had to burst out into laughter (of course it is not funny at all).
But that really, really does remind me of my father. He has become very bitter over the last few years. Actually I can’t remember him NOT having this bitter side… Anyhow, he isn’t paranoid like that, but he has been very ill and I think he believes that we would be all happy if he just died. When he accuses us of those terrible things, which are at the time very hurtful, because my mother and I love him very much of course… we can’t help but laugh about it afterwards.
It is just … too absurd.
If you have to deal with him closely much longer and if it still does hurt you, maybe you could call up a help line or read up on how to deal with the elderly with that condition.

I have a relative, who I’d rather not name, who seems almost exactly like your father. He even has the same paranoia—he will often think the food we make him is poisoned or that others are staring in at him through his windows. While he can tolerate some members of the family, others he will not speak to and will blatantly insult, for no apparent reason.

Medication does help though, at least for him.

The hardest thing is knowing that there’s nothing you can do, really. Has your father been diagnosed with a mental disorder? Getting a doctor’s opinion is usually helpful, even if you’re against medication. At least it’s therapeutic.