A smritis or code of conduct composed by Sage Atri defines Brahmin Hood very clearly.+

The one who has realized the Brahman (God) is Brahmin, not the one who is born in the Brahmin caste.

The Vedic system did not have a castes system.  Hinduism is nothing to do with the ancient Vedic religion or Santana Dharma. 

The caste system was a fake created in the name of Hinduism. This non-Vedic belief system called Hinduism has created hatred in the low caste Hindu for the higher caste. 

Hindus indulge in non-Vedic beliefs such as idolatry, ancestor worship, pilgrimages, priestcraft, offerings made in temples, the caste system, untouchability,, and child marriages. All these lack Vedic sanctions, therefore, Hinduism is not Ancient Vedic religion or Santana Dharma. 

All Hindus indulge in non-Vedic practice barred by the Vedas introduced by the different founders of the different sects of Hinduism at different times, whereas the Vedic religion or Santana Dharma is ancient and has no founder. Many followers of Hinduism do translate the Vedas to fit into Hindu thought by changing the translation to reflect the beliefs of monism, reincarnation, the caste system,, and the absence of animal and human sacrifice. However, these poor translators.

In the Vedic era, a Brahmin was a person who had acquired Self- knowledge or Brahma Gnana Atma Gnana. This was an extremely difficult path of the discipline of body, mind, and intellect, and people irrespective of their birth or class, who were dedicated to such an austere life, were recognized as Brahmins. 

A great example of this tradition (that a person becoming a Brahmin, rather than born as one) is the case of Vishwamitra, a warrior (Kshatriya), who became a Brahmin after attaining Atma Jnana or  Brahma Gnana or Self-Knowledge.

A smritis or code of conduct composed by Sage Atri defines Brahminhood very clearly.

"By birth, every man is a Shudra (an ignorant person). Through various types of disciplines (samskaras), he becomes a dwija (twice-born). Through the studies of scriptures, he becomes a vipra (or a scholar). Through the realization of supreme spirit (Brahma jnana), he becomes a Brahmin.”

The belief that people born in the Brahmin caste, automatically become Brahmins, is a much later concept in very ancient India.  Thus, Brahmin means not caste but one who has attained Atma Gnana or Brahma Gnana.  

The one who has realized the Brahman (God) is Brahmin, not the one who is born in the Brahmin caste. Anyone can become Brahmin by acquiring Brahma Gnana. 

The very concepts of castes by birth, upper/lower castes, superior/inferior castes, outcastes, untouchables, Dalits, etc. are clearly prohibited by Rig-Veda”.

A Brahmin is not a Brahmin merely because he is born out of a Brahmin mother’s womb. Nor he is a Brahmin merely because he is born in the Brahmin caste.  Brahmin is not Caste it is the state of God. Anyone can become a Brahmin by acquiring Self-knowledge or Brahma Gnana or Atma Gnana.

A Brahmin has acquired Self-knowledge or Brahma Gnana or Atma Gnana or one who is free from ignorance.

He has got rid of the ignorance; He has traveled beyond all bounds of form, time, and space. He is no longer tied to the illusory form, time, and space.  A person who has acquired Advaitic Gnana is a Brahmin, not a person who indulges in priestcraft.

A Brahmin has got rid of the strap of ignorance by acquiring Self-knowledge or Brahma Gnana or Atma Gnana.    A Brahmin is the one who freed himself from the dualistic illusion.

A Brahmin has broken all links with the illusory form, time, and space by acquiring Self-knowledge or Brahma Gnana or Atma Gnana.

Brahmin has taken off the cross-bar of ignorance. He has become aware of the truth is hidden by the ‘I’.

A Brahmin is abused and insulted by the ignorant. He is tortured, imprisoned,, and bound up by the ignorant. But he endures all these without being provoked or without losing his temper.

A Brahmin has patience as his power and his firm conviction about the truth, which is hidden by the ‘I’.

A Brahmin is free from the ignorance of his true existence. He is not the performer of religious worship and rituals. He is not a scriptural scholar. He is restrained.  He is fully aware of the fact that his individual experience of birth, life, death, and the world is an illusion created out of the Soul, which is present in the form of consciousness.

The Brahmin does not belong to any religion, caste, race, or nationality because he does not belong to the domain of form, time, and space.  He, even being within the domain of the form, time, and space is not of the form, time, and space.

The water does not get attached to the surface of the lotus leaf. The mustard seed does not get attached to the point of a needle. In the same way, the Brahmin does not get attached to religion caste, race, or nationality.  He is non-attached from the world in which he exists even though he is in the world; he is not of this world.

A Brahmin has become aware of the fact that the world in which he exists itself is an illusion created out of consciousness.  Brahmin is the one who is aware of the fact that Self-knowledge or Brahma Gnana or Atma Gnana frees the Soul from the cage of the dualistic illusion.

A Brahmin possesses profound wisdom. He is full of insight. He is capable of discriminating the right path from the wrong path. He has reached the highest state.

A Brahmin is the one who has established the reality of his true existence. He is not attached to the world in which he exists.

A Brahmin is the knower of Brahman.  His speech is true. His words are well-meaning, constructive, and not harsh. By his words, he will not give offense to anyone. Nor will his words provoke people. He silently shares the Self-knowledge or Brahma Gnana or Atma Gnana.    

A Brahmin is the knower of Brahman. He has no attachments to the ‘I’ - He has no spiritual doubts due to his right awareness, He has entered the deathless existence.  

 A Brahmin has traveled beyond form, time, and space and realized the true existence is formless, timeless, and spaceless. 

The Soul is like the moon at the full - spotless and free of blemishes. The Soul, the Self is pure, calm, serene, and exceptionally tranquil.

A Brahmin has crossed over the quagmire of passion. He has gone beyond the difficult terrain of the dualistic illusion that is hard to traverse and has crossed the boundaries of ignorance. He is fully and totally reached the other shore.

He is in self-awareness. His spiritual doubts are resolved. His quest is over He is no longer given to grasping. He is cooled.

A Brahmin is the one who has realized Brahman.  He has given up the bonds that bind him to humanity. He has gone beyond the bounds of form, time, and space. He is disengaged from all bonds of the dualistic illusion.

A Brahmin is the one who has given up the religion and religious idea of God and religious rituals. He has also given up yogic Samadhi and the practice of meditation. He has achieved total tranquillity of the formless, timeless, and spaceless existence. He has conquered the effortless reality with his mental effort.

A Brahmin knows the experience of birth, life, death, and the world is an illusion created out of the Soul, which is present in the form of consciousness.  He is not attached to the illusory experience of birth, life, death, and the world.

He has reached the destination which is beyond the illusory experience of life, death, and, the world. He possesses the knowledge of the essence which is the cause of the world in which he exists.

The path of truth is neither of Gods, nor of the religion, nor of the humans. All taints of ignorance are totally eradicated in the Atmic path. Those who tread the Atmic path have attained the highest spiritual knowledge.

He is a great Sage as he has realized the essentials. He has conquered the truth which is beyond birth, life, death, and the world. He is devoid of blemishes. He has washed away all the ignorance. He has awakened to the essentials.

He has his higher awareness. He has reached the state of a Sage. He has achieved the final perfection. :~Santthosh Kumaar