"Aren't you a little old for imaginary friends?" is one of my favorites.
The legitimate evidence that any ' holy book ' is the words of a god given to men remains a constant zero!
The biblical jesus is just another man made fictional character, incapable of loving, doing or giving anything other than the man made writers make it do in their various story books, bible included.
A reply in Latin seems best. After all most of those who use the remark in question won;t know what it means anyway. Perhaps, "Quid est veritas" would do the job
I don’t know, I think I’d probably use something more along the lines of that old Dr Pepper TV commercial; I’d break into song with:
Jesus loves me, Satin loves me, Mama loves me, Daddy loves me, wouldn’t you want to come and love me too?
I just walk past those crazy people in the street. It's best not to make eye contact.