Brahmin is any person who knows Brahma(God or Oneness). If somebody claims I am brahmin, because my I wear a thread or government asked me to put brahmin as caste. Then they do not know hinduism.
As somebody rightly said, try to become brahmin, again not today's so called brahmin , but brahmin described in vedas who are supposed to be selfless and realized that god is in every human being.
Valmiki was born as chandala, but he became brahmin by deeds. Similarly so many asuras were born to brahmin selfless fathers, but they became low caste by deeds.
It is simple, you belong to each caste by what you do not by birth.
