To answer that question I believe we need to figure a few things out first. One) What does it mean to be a christian? Two) In the end who is going to be the final judge?
First to answer what is means to be a christian. Lets first take a look at what the word is implying. Christian implies that we are followers of Christ and His teachings. If I am a follower of Christ and His teachings what does that mean? It means that:
1) I am going to Follow the example Christ set. (John 10:14 "I am the good shepherd, and know my sheep, and am known of mine." If we are Christ sheep we are going to follow him.
Finally 3) We are going to live our lives according to our beliefs. We seek Christ through the scriptures (Old Testament, New Testament, and Book of Mormon) and what the spirit tells us. We must always be looking for the promptings of the Holy Ghost to help us get on and stay on the correct path. How do we know the spirit well "...the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance." (Galatians 5:22-21)
And to finish off we must remember that it is not our place to judge. "Judge not that ye be not judged." (Matt. 7:1 and 3 Nephi 14:1) Who are we to say who is Christian or not. We cannot see that hearts of intents of others. We cannot be a perfect judge. "...God shall judge the secrets of men by Jesus Christ according to my gospel." Romans 2:16 "...names are written in heaven, where God and Christ are the judge of all." (Doctrine and Covenants 76:68, emphasis added)
It is only the opinion of Christ that matters in the end. All else is naught to the judgement of Christ, HE who paid the price of the worlds sins. Corinthians. 6:20 "For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God’s."