I don't think we can improve upon Augustine's understanding of evil as the privation of good. I like what Jonathan said. We are evil to the degree that we serve idols rather than God with our rational choices. Our choices serve some kind of "good" as long as they are rational, but they are only truly good if they serve God's will. We can't even do what's good for ourselves without being centered around God because we otherwise serve false, socially-constructed demonic selves that the world has superimposed upon our true created selves in order to make us into consumer slaves.