The social media world is full of small biographical statements of people describing themselves as "disciples" or "followers" of Christ. Those particular titles outside scripture were never on my radar until after the social media movement, but they make perfect sense to me. To call oneself a "disciple" is a bold statement that should not be taken lightly. Those that carried the term disciple in the scripture did not claim it for themself but found themselves in the position of a disciple.
1. Disciples are called. The disciples were a handpicked group of people picked by God to be used for His purpose.
Mark 1:17 KJV
 And Jesus said unto them, Come ye after me, and I will make you to become fishers of men.
2. Disciples are obedient. They are obedient to their calling and willing to leave their "old lives" behind.
Mark 1:18 KJV
 And straightway they forsook their nets, and followed him.
3. Disciples operate under the authority of their master.
Matthew 10:1 KJV
 And when he had called unto him his twelve disciples, he gave them power against unclean spirits, to cast them out, and to heal all manner of sickness and all manner of disease.
Matthew 10:24 KJV
 The disciple is not above his master, nor the servant above his lord.
4. Disciples minister.
Matthew 10:7-8 KJV
 And as ye go, preach, saying, The kingdom of heaven is at hand.
 Heal the sick, cleanse the lepers, raise the dead, cast out devils: freely ye have received, freely give.
5. Disciples live by faith.
Matthew 10:9-10 KJV
 Provide neither gold, nor silver, nor brass in your purses,
 Nor scrip for your journey, neither two coats, neither shoes, nor yet staves: for the workman is worthy of his meat.
6. Disciples use wisdom.
Matthew 10:16-17 KJV
 Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves.
 But beware of men: for they will deliver you up to the councils, and they will scourge you in their synagogues;7. Disciples have no fear.
Matthew 10:31 KJV
 Fear ye not therefore, ye are of more value than many sparrows.
8. Disciples sacrifice.
Matthew 10:22 KJV
 And ye shall be hated of all men for my name's sake: but he that endureth to the end shall be saved.
Being a disciple is difficult, but the reward for those that endure is heaven. Calling oneself a disciple should not just be in your Twitter bio, but a lifetime commitment to cause of Jesus Christ. Of the 11 disciples that were left after Judas, 10 died at the hands of an executioner. Those that are true disciples do not need to declare themselves one, but their fruits will reveal to the world their position in the Kingdom of God.
Acts 4:13 KJV
 Now when they saw the boldness of Peter and John, and perceived that they were unlearned and ignorant men, they marvelled; and they took knowledge of them, that they had been with Jesus.