I have answers to proselytizing Christians (and others).

Christian: "Have you accepted Jesus Christ as your personal savior?"

Me: "I'll leave that as a matter between Jesus and me."

At other times, I explain to the proselytizer (Christian or otherwise): "I was born to a Jewish family and raised in the Jewish faith. I no longer practice Judaism. I could convert to your religion and not practice it. But, if I'm going to not practice a faith, I'd be better off sticking to the faith I am familiar with and already know how to not practice, rather than trying to learn how to not practice an entirely new faith."