There is no legal document that proves anyone a Christian, as there is for nationality or other statuses. So Christian status may indeed be said to be dependent not on documentary evidence, but on behaviour,
So someone who describes themselves as Christian and genuinely believes themselves to have accepted Jesus as their saviour, would cease to be Christian if they did something immoral? You seem to trying have your cake and eat it. You are simply trotting out the fallacious line, unaltered.
Like it or not, "Christian" is commonly applied as a noun. You seem to be trying to use it as an adjective, with a definition synonymous with "moral", a practise which I consider disingenuous. If you define "Christian" as "moral", then naturally, all Christians are moral. You are simply trying to define Christianity into a moral position, by dishonest use of terminology.
There is no legal document that proves anyone a Christian
And yet there is such a thing as a Christian. Yes or no?
If yes, do some of those Christians behave immorally? Yes or no?
Mutate and Survive
"A curious aspect of the theory of evolution is that everybody thinks he understands it." - Jacques Monod