"A rockstar is a different thing. PM should not do such things. I am not against a rockstar but the PM behaving in such a manner is not right. He should maintain the dignity of the post," Singh told reporters here.
He claimed that the one-year of BJP-led NDA government was disappointing.
"Yesterday, he (Modi) presented the report card of his one-year governance, but did not utter a single word about achche din," he said.
He said that the promise was to create 2.5 crore jobs every year but in 2014 only four lakh were created.
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Singh said that he did not say a single word about 'Make in India' as manufacturing has declined in the last one year.
"He has not only forgotten his promises but yesterday Modi established that he had nothing to say about farmers and the youths," he said.
He refused to have an alliance with any other party and said that the RLD was preparing to contest on its own in the state assembly elections due in 2017.
On BJP deciding to organise 200 rallies to mark its one- year in the office, Singh said that there was no enthusiasm among the people.
The RLD chief said that what his party did for farmers was not done by any other party.
He said that there was not much hope from the merger of six parties of the erstwhile Janata Parivar.
"But I will say that the manner in which Lalu Prasad, Nitish Kumar and Congress contested by-elections in Bihar, it will give an alternative to the people," he said.