In fact, if some moral law doesn't exist, then you can't even call a person evil because what an evil person is, is a person who consistently and persistently violates a moral law. Maybe it isn't obvious to you that torturing babies just for the joy of it is immoral, and if you would say that then I don't think that you have a different morality, I think something is wrong with you. You are a couple sandwiches short of a picnic. You are missing some parts. You ought to get help, frankly, because there are some things that are just obvious.
Forcible rape is wrong.
That strikes me as rather obvious, and that's why we say people who are rapists are evil people. Now, both of those statements are dependent on the fact of the existence of a moral law. Now, I'm kind of going on the assumption that you agree that there is at least some moral law out there. One of those two illustrations was patently obvious or maybe something else that you can think of, like mercy is a virtue, or kindness is good. These are moral statements and they reflect a law that is real.