Here is another article I found interesting while researching "evil". The actual article is long but below I'll give you a recaps of the important parts..
Human Evil: The Only Kind There Is
In summary, evil involves 2 necessary ingredients:
1) a scapegoat (because "somebody" has to pay for the destructive behavior), and
2) militant evasion
(because evil or destructive behavior is antithetical to the kind of existence -- ie. productive existence -- which is proper to man).
Now there are definitely degrees of evil. Some degree of evil is all around us. I notice some degree of evil almost every day. This does not mean that I (or anyone) must retreat and become a hermit -- in order to extinguish all evil from our lives. That choice would be sub-optimal. There are too many folks who have some evil in them, but still harbor some good, for us to write them off wholesale -- upon their first evil act.
The things to watch out for are a person who militantly avoids introspection or any questioning of their motives, while simultaneously offering up others as sacrificial animals. The key is consistency. Truly evil folk are completely consistent in their behavior. They are almost predictable.