"It is in fact 'chai pe chugli' (backbiting over tea)," Kumar said in his caustic comments on social networking website Facebook.
The Bihar Chief Minister, whose aversion to his Gujarat counterpart is an open secret, said in fact people expert in "hawabazzi" (making inflated claims) indulge in gossiping over tea.
Kumar, who is the driving force of JD(U), led the break up with BJP over nomination of Narendra Modi as the party's Prime Ministerial candidate. The separation left JD(U) alone in government in Bihar.
He said in his home state he has initiated a programme called "kam ki charcha" (discussion over work) in which people talk over good and bad things about the developmental works being undertaken in the state by his government.
People across the world are talking about rapid strides Bihar is taking in recent days, Kumar said. Bihar has drawn appreciation from leading personalities like the Dalai Lama, Bill Gates and several other dignitaries from UK and European Countries, he said.
Leader of Opposition in Bihar Assembly Nand Kishore Yadav said the Chief Minister's adverse comments reflect his "frustration" and proves he is suffering from "Modi phobia."