I must admit I get a great kick out of those who state their definition of a Christian as if they got it direct from Christ himself. They are entirely free to limit their recognition as Christians to those with whom they agree, but with all due respect I submit that they need a little work in the humiility department.
Jesus' parable of the wheat and tares illustrates two very important points:
1. It may not be immediately obvious who are his true followers.
2. Not everybody who claims to be a Christian will be recognized by him as such.