Christianity isn't about doing what you want- it's about how Christ needed to die because we cannot follow these rules. I think someone who thinks they are a "good Christian" is already making the mistake in thinking that.

Luke 18:19

And Jesus said to him, “Why do you call me good? No one is good except God alone.

1 John 1:8

If we say we have no sin, we deceive ourselves, and the truth is not in us.