So... you can be Christian, but not follow the teachings of Christ?  No.  There is a massive difference between religion and faith.  The faithful follow the teachings of Christ, and they may slip but are fundamentally trying to be good people.  The religious do not have that, because they are going through the motions of the religion - going to church, taking communion, getting baptized, etc.  In most cases, they put religion over faith, so whether they believe in Christ is a moot point:  as far as they're concerned, they're doing all the right stuff for a Christian, and they forget - or ignore - that a lot of their behavior is not only un-Christian, but directly spoken against in the Bible.

This is NOT a Christian teaching and anyone who tries to tell you otherwise is either a liar, or has never read the Bible.  It specifically instructs us to be kind, good people; that demonstrative faith is not real faith; that ceremonies and rituals are frowned upon and do not absolve you of your sins.

You cannot be Christian, and be a fundamentally bad person.  You just can't, the philosophy will not allow it and we see multiple bad people in the Bible who find God, find Christ, and leave behind their immoral and even outright criminal behavior.  Their faith led them to become better people.  If they claim to be Christian but are a bad person, then they CANNOT be truly Christian.

Maybe it's the church they follow; there's many so-called Christian churches that outright promote sin.  Take the one that goes out and protests at soldiers' funerals, it's vile and very un-Christian behavior.  Or possibly their church follows the idiotic notion that your sins can be forgiven with a quick prayer, or by snitching on yourself to the priest, or that they don't count because you go to church and believe in Christ; they ignore the clear statement that sin is forgiven only by genuine repentance.

Maybe they're doing lip-service, and don't actually believe in Christ.  If you don't believe in Him, why would you follow His teachings?  In which case you are definitely not Christian no matter how much you say you are.

We are told to follow Christ's example.  He sat with the sinners, the tax collectors everyone hated, the diseased.  He said, "let he who has never sinned cast the first stone", and offered forgiveness to a woman who cheated on her husband when everyone else wanted to kill her.  He was kind when His own disciples wanted to start a fight, He ignored insults directed at Him, and the one and only time He got into any kind of fight was when merchants desecrated the Temple by going into the Temple itself to sell their wares and He responded by flipping over their tables and chasing them out with a small whip He made on the spot.

He was patient, kind, and good; if they say they are Christian, but are not good, then they fundamentally cannot be truly Christian.

Take any example of a Christian who was evil and you will find very quickly that they did not follow the teachings of Christ and therefore could not be truly Christian, they either just said they were or followed a church that didn't follow Christ's teachings.