What's a bad person with bad dispositions, if not someone who does bad things?

Well, in practice most of us do make these sorts of judgments. We don't think a bad person stops being a bad person when we imprison them, for example, even if they are thereafter unable to do bad things and therefore don't. Which suggests that we have some notion of a bad person who isn't doing bad things.

This may not be justified, but I'd be very surprised if it were so alien to you that you don't understand it.