Why do you have to respond to some a$$hat who screams at you and calls you names? Is he your supervisor? If not, ignore him. Nothing you say is going to change his mind or bring clarity to his thought processes.
There's no reason to engage this guy further. I wouldn't even reply to his email.
And if he persists, file a complaint with HR.
He’s a physician in our department. I’m a nurse anesthetist so he is sort of above me. The thing is, if I don’t give him an answer, I’ll never hear the end of it. He’ll take it as me conceding defeat. He’s a pain in the ass.