The psalmist here is not writing about the person who denies the existence of God. That would have been unheard of in ancient Israel. But there were, then as now, plenty of people who went about their everyday lives as if God could not see what they were doing. The Hebrew word for that kind of person is “nabal” and a man of that name died for his refusal to give food to David when he needed it (1 Sam 25).