The man responded with:
"The fool says in his heart, “There is no God.” They are corrupt, they do abominable deeds; there is none who does good" (Psa. 14:1).
This is a quote from Psalms 14 which is a popular retort that I've heard believers use towards myself and other atheists. So I decided to respond here.
The Psalms are a collection of poems, lamentations, and songs that are either credited to King David of Ancient Israel or is said to be about him. In this particular psalm, the author is talking about a particular situation that he is dealing with. In the previous psalm, the author lamented about Yahweh not talking to him and "hiding his face" from him. It has elements of a teenage love drama.
In 14 it talks about a "fool" who says there is no god "in his heart". I told the apologist that it is impossible for anyone to say anything in their heart. This is a fact. I fully understand that this is hyperbole and that the Psalm has to do with events happening in the time it was written. King David had a curious "relationship" with the voracious monster Yahweh. Thus this writing comes off as just a comparison between people the author claim are evil and those who believe in Yahweh. There is a footnote that says that the word "fool" is meant to denote one who is morally deficient.
It seems that when a Christian uses this, it is meant as a slight. But by no means am I a fool; even in the morally deficient sense. The atheists that I've encountered tend to be more intelligent and knowledgeable that the average Christian. There have been polls that have demonstrated that atheists tend to know and understand religious books better than believers. There tend to be less atheists in prison/jail as well.
In the past, I've asked the person using this verse against me if they think they are calling me a fool. Usually they quibble but it is clear that they intend to insult me. This is fine because normally the person does not know me, my level of intellect, or how moral I am.
In the atheist community, the use of Psalms 14:1 is so well known that a witty response has been formulated.
"If the fool figured it out, what is taking you so long"