Very good question!
Evil, in Buddhism, becomes a situational response one has within one's place in samsara. We can choose to become trapped in samsara, unconsciously accumulating bad karma by wrong action and with harmful intent (which defines evil) -
Or we can choose to develop actions that are truly not "natural" such as compassion, love, forgiveness, and patience toward one's enemies. These choices in the numberless opportunities life provides us brings us closer to liberation or rebirth into samsara.
I apologize if the above sounds like I'm proselityzing.
My above statements are relevent in that evil can dwell in our hearts long before any actions bear it's fruit. The Five Precepts are a good start:
1) I will be mindful and reverential with all life. I will not be violent nor will I kill.
2) I will respect the property of others. I will not steal.
3) I will be conscious and loving in my relationships. I will not give way to lust.
4) I will honor honesty and truth. I will not deceive.
5) I will exercise proper care of my body and mind. I will not be gluttonous nor abuse intoxicants.
The Buddha then spelled out specifically the Eightfold Path that includes not only what is Right Action, but Right Speech and Right Thought.
Therefore, in my tradition, evil does not exclude minor infractions such as yelling out of anger at your spouse or your children. It is a much broader definition that encourages the Buddhist practitioner to consistently practice toward enlightenment in order to not only escape the wheel of samsara, but to eradicate evil toward all sentient beings, and to plant the seeds of compassion for the world's benefit.
Again, I hope I'm not perceived as trying to "sell" my beliefs on to anyone here.
Peace,
Mystic