How about:
A bad person is someone who only cares about self-gratification (of some kind) but does not care if others are harmed in his pursuit of self-gratification.
An evil person is someone will deliberately set out to harm other people for self-gratification and then take pleasure in observing the damage he has caused.
Well there's a funny thing.
I've always considered evil to be sadism - not
just causing pain
per se, because over the course of a fairly long life (to date) sundry and divers medical professionals have done that incidentally, with a greater good in mind. I have never dislocated a limb. I have heard and would imagine that resetting such is perhaps briefly but intensely painful. But there is a greater goal in mind, so it can't be evil.
No, I think evil is sadism; the glorification of shame and humiliation and above all else pain purely for the sake of being a spectator of the preceding.
I am sorry to say that I have (have had) visual evidence of the uttermost worst of this by humans to other humans and also to non-humans, in ways that I refuse to describe in detail. According to my own personal definition, some humans are simply evil. Evil as far as I understand it; the delight in suffering of another for the sake of that delight in its own right.
There are reasons I'm not and refuse point blank to call myself a humanist, and I flatter myself that I've seen most of them. Some humans are just evil.