"BJP is drunk with power and is making brazen comments on me and other opponents...But their 'ghamand' (arrogance) will not last long," Kumar said addressing an election rally here in support of Congress candidate Ajit Sharma.
"Jab Ravan ka ghamand nahi raha to BJP ka kya rahega (when arrogance of mythical Ravana did not last how come that of BJP will sustain)," Kumar said about his former companion.
Kumar, who floated the idea of alliance of secular parties comprising JD(U), RJD and Congress to take on BJP, addressed a joint meeting with Congress General Secretary C P Joshi.
Kumar, who resigned as Chief Minister of Bihar in the wake of severe drubbing in the general election, said BJP came to power by successfully selling their "poisonous thoughts" which aimed at dividing the society on caste and religious considerations.
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"To mitigate the impact of these poisonous thoughts of BJP which is fast gripping the society after they came to power at Delhi we have developed a 'medicine' of alliance between JD(U), RJD and Congress," he said.
Kumar slammed Narendra Modi government without naming him for "forgetting" the tall promises of providing special category status and special attention to Bihar to spur its growth.
"They had promised to win back our land acquired by China and chase away Pakistanis...What happened to them?" he said in a sarcastic tone.