Without an absolute standard of good, their can be no real evil. It would be all up to the individual what is “good” and what “evil” is.
Hitler liked killing people to aid in the evolution of his race, Mother Teresa liked helping people who could not help themselves. Without an absolute standard the best we could say is that we like Mother Teresa’s version of morality better than Hitler’s.
Most evil is “good” in someone’s mind. Few people ever get up in the morning, and think “How can I be evil today?” Instead they think about their own wants and needs, and how they can get what they want. Without an absolute set of standards to judge morality by, any way that they can come up with is OK. You might not like their way, but who are you to say?
For more info please read: Relativism: Feet Firmly Planted in Mid-Air