Since the Bible doesn't say 'real' or 'true' Christian. I'd rather speak of Christians in deed and in truth, vs Christians in name only. Confessing faith in Christ from the heart, vs with lips only.Real Christian would be one who has received as their Savior and Lord Jesus, now indwelt by the promised Holy Spirit, and agrees with the cardinal truths, such as God being Trinity, Physical resurrection, actual Second Coming etc
Mar 7:6 He answered and said unto them, Well hath Esaias prophesied of you hypocrites, as it is written, This people honoureth me with their lips, but their heart is far from me.
1Jo 3:18 My little children, let us not love in word, neither in tongue; but in deed and in truth.
As I said at the start. The subject has nothing to do with being either one or the other, and especially not with making judgments about one another. It's only about what is a Christian, and so can be called a Christian on earth: I've given the Scriptures, that call Christian, anyone confessing faith in Christ, and calling Him Lord.
Whether we are an obedient elder, or disobedient prodigal, is beside the point. Even as Scripture calls them both sons, so does Scripture call us all Christians.
According to the admonishment of Scripture, I would avoid Christians living riotously, but pray for them as a brother. And so long as they continued to confess faith in Christ, I would never call them a non-believer and not a Christian.
It could help to understand this simple point, by making difference between calling someone a Christian on earth, because they call Him Lord, vs the Lord Himself calling someone Christian in heaven, where all that call Him Lord love Him as Lord. That is where only Christians in deed and in truth will be called Christian forever:
Rom 11:26And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: For this is my covenant unto them, when I shall take away their sins.