Twice-born is dvija: the second birth is not the upanayanam, but the awakening of kuNDalini.
Who is a brAhmaNa? One who knows Brahman.
What is varna sankarah that Sri KRShNa refers to in the Bhagavad GIta? It is the admixture of castes not only by miscegenation, but by brAhmaNas doing business on Wall Street.