Jawahar Lal Nehru -
because as the first PM he should have set a very high benchmark but he failed miserably and instead set the tone for corruption, unaccountability, nepotism, sectarianism, foolhardiness, vengefulness, deceit, and you name it.
Having said that, I will consider I K Gujral more worst than Nehru as he set about destroying the external intelligence (humintel) abilities totally. Even an enemy could not have achieved what he did as PM of India.