Thanks for the question. I'll happily respond.
People who purely seek Christ call themselves Christian. And, when you seek Christ, you are called to obey the morality of Christ.
You seem to be referencing a person who is trying to "play" or "trick" God... someone who thinks they can label themselves a Christian but then go about openly sinning without any humility, guilt, or regret. All humans, Christian and non-Christian, sin. We Christians go to church on Sunday knowing we sinned. However, the difference comes at this; Christians identify their actions that are outside the morality of Christ as sinful, and repent, and then will intend to sin no more. That is how forgiveness works. The non-Christian will not attend a service, not humble themselves, and feel they have done nothing wrong (and that's understandable as they don't believe).
I often run into outsiders of the faith who try to hold anyone who calls themselves a Christian against the faith. I immediately ask them to remember what Christianity is, or learn what it is, and then compare it to what the people they are trying to brand onto the religion do. That's a good starting point. It's simply an uncompelling waste of time to explain how people with morals that are clearly outside of the faith shouldn't be held against the faith.. when the outsider can simply use their common sense. Usually, however, this is done to attack and malign the faith in a very intellectually dishonest fashion. But again, it's a boring practice to address, and a very sad measure of their intellect.
