Then why are you friends with this person if you find them narcissistic and delusional? That is called a toxic relationship.

Just tell them that you know they mean well, but that you want them to stop. Really. It's up to them then if they want to test your friendship to destruction.

SE
Street Epistemology
To do this you enter into a one on one conversation with the person using the socratic method. In this you nicely and calmly ask them what they believe, and why they believe that.
DO NOT DEBATE!
DO NOT SHOOT DOWN THEIR IDEAS!
BE POLITE!
Just ask them WHY, politely and nicely, again and again.

SURPRISE!
They don't fucking know why they believe, they just do.
AND they don't know they don't know.

Watch a few of these to get the idea . . .
Read Peters Book.

The word you are looking for are the words you just posted

I have found that it can be stressful associating with morons. Try to avoid them and seek out the company of more enlightened people.

One opens ones mouth and utters the desired words.

In your situation I would be be tempted to say that I can't make myself love someone. They have to earn my love. But if they are a delusional asshat most of it is a waste of breath. My tendency these days is to tell someone who is truly impertinent that I will not have any more conversations with them on this topic and leave it at that.

Let them know you're an atheist or agnostic. (or whatever you are?)

Why are you friends with a narcissistic delusional missionary?

I agree with the others that said something like, "tell them to fuck off".

I work up through a progression from nodding and smiling and saying "you know, I'm really not religious" to politely saying "not interested" and eventually (with many intervening steps) to "please stop and STFU about your delusional beliefs." By the time you get to insulting someone for being an idiot who believes in "fairy tales" (and I like to use that specific expression - it seems to really put off theists) they usually get the idea that you're not tolerating any further proselytizing.

OK ! Just tell them to F.CK OFF should do it !

It really sounds like you don't like this person and should not be friends with them in the first place. I'm just judging by your language and tone. But if they're being rude about it and will never stop, you have the right to be rude right back.

"I've read the bible too much to believe it actually true" if i wish to be gentle or simply
"I'm an atheist," seems to work well for me. It may depend on the part of the country your in.

By their continued pressure they're showing disrespect to you.
. There's no polite way to tell someone to "fuck off with that shit"