Sorry, but that was a trick question. In actuality, there is no such thing as a good Christian. Jesus said that only God is good (Mark 10:18, Luke 18:19). To call oneself a “good Christian” is to directly contradict Christ himself. Now, that doesn’t sound like something a good Christian would do. 😉
Perhaps what people mean when they say they are “good Christians” is that they are Christians in good standing with their church (for whatever that’s worth). I don’t know. But at least to me, it doesn’t come off sounding like that.