My thought would be that nothing is good outside of God. Even our most righteous acts are like filthy rags before God.I'm not sure. I'm not suggesting you're wrong, but I think it's a bit more complex than that.
I think only good can come from God. I think many non-Christians who do believe in God (namely Jews) actually do try to pursue the good that they know comes from God. While they are wrong in rejecting Christ, we do have a legitimately common God and common enemy...and we know where goodness comes from.
But taking it a step further, I also think even agnostics and atheists can know morality. They can't justify it or explain why such-and-such is good, but they can divide it. They just can't understand where goodness comes from, but they often agree that it is right to help someone who has fallen and reject something that is clearly wrong, like rape. I'm speaking generally of course because there is still much disagreement on other things. For argument's sake, let's keep it simple and look at the principle.
I do think God's goodness does extend even to those who can't see where it comes from.
I'm only making a suggestion that perhaps evil is only the lack of goodness. And if even those who don't know where goodness comes from can actually do what is good purely because it is right, then perhaps it's not evil. But actions, even with good intentions, can be very misguided. And misguides are a subject of imprudence, not evil.
Maybe there are different levels of evil, but I would assume that anything not done for God, is against God. Anything against God is evil. Any speech that comes out of our mouths that is not pleasing to God, I would assume is evil. If its coming out of my mouth, whether its a joke, or pretending, isn't it in my heart?
The bible says this about the tongue:
Can both fresh water and salt water flow from the same spring?