... We are again talking about whether or not ______ is a Christian ...
Fixed it for you.
A Christian is anyone who self-identifies as a Christian. Period.
Now, if someone says "______ is a not a true Christian" what do they really mean? They mean that they are not the same kind of Christian.
Which is fine, imho, as there are hundred (if not thousands or millions) of different ways to be a Christian.
In fact I would even go so far as to say that everyone that self-identifies as a Christian is different from everyone else that self-identifies as a Christian, that it means something different for each and every one of you.
This is why there are so many sects, why every priest, pastor, etc goes about it differently. Every Christian is different.