We all know people with big egos, who are self-centered and all for themselves--the "me" people. But someone truly evil? That person seldom appears in our lives. However, every now and then, a person will enter our garden of Eden who is truly evil from birth.
Professionals blame their behavior on their upbringing, their home life, their environment--any number of reasons. The real answer is, they really don't know why they're like that. Sigmund Freud categorized everyone into a neat box with his diagnosis. But other than the bad seed theory, no diagnosis exists. Hopefully, you will never have one of these people in your life.