Christians today have a bullet list of things a Christian must believe. To believe all of them equals 'Christian', to not believe one or more equals 'non christian'. Numerous groups such as Jehovahs Witnesses or Christadelphians may not agree with one or more of these statements and are therefore not considered christian by the main evangelical groups.
In the Book of Acts Christians are so named because they were' Christ-like', which itself is a subjective measurement. Jesus is said to have said that obedience constitutes being a Christian. These two definitions do not require belief in a bullet point list.
It is perhaps disturbing the notion today that believing in the wrong things, being defined as heresy, results in being condemned to hell. Even believing 95% of the party line is not enough to be saved. The idea of believing incorrectly resulting in eternal damnation is contrary to common civil law and common sense. Belief is subjective, influenced by the opinions of others, and dependent upon the environment one finds oneself in. Action is measurable and not subjective and common sense tells us that action is the measure by which we should be judged, being what our legal systems are built upon rather than thought crime. Thus definitions of Christian today make little sense and are contrary to the definitions proposed by the citizens of Antioch and those of Jesus himself.