Everyone acts selfish. Everyone. Humans, animals, everyone. That's the fundamental truth.
Holdfast got close to the point:
With that caveat, I think there are very few people who actively approach life with the intent of worsening other people's life experiences. I guess that's equivalent to a conventional definition of good, so that's what I ticked, but really it's all semantics.
Good or bad is all about what happens to others when you're acting selfish. Are you destroying the career of a coworker because you want his job, for example? Or are you letting things be, find another way?
And then good and bad is ill-defined. Why is murder bad, for example?
When is murder bad? How can it be, that in Christian faith, God first killed all first borns and countless of people, and then declared "Though shalt not kill"? In other cultures, ritual murder was and/or is gladly accepted. Murder on the battle field is perfectly okay, unless you violate certain
"rules of engagement", made up by other people. In the United States and other countries, criminals are essentially murdered by state officials as punishment. In Iran, criminals are stoned to death by civilians as punishment. Why is it "good" to kill criminals? Who decided that? And is that decision right?
In the end, in this example, it's the "need for justice". And "justice" means "revenge", which is just compensation, and compensation is a self-serving need. Someone murders your loved one, and you want "justice". For some it's okay if the murderer gets behind bars for the rest of his life. Others need to see the murderer get killed. Eventually, it's all about what makes you feel better. And what makes you feel better is considered "good".