Police chiefs have admitted they are responsible for the deaths of some 600 drugs suspects since July, with local media suggesting the true number could easily be more than 1,000 when vigilante killings are taken into account.
Last week, two UN human rights experts urged Manila to stop the killings, saying they amounted to a crime under international law. President Duterte has denied the government is responsible.
"I will prove to the world that you are a very stupid expert," he declared during a late-night news conference on today.
He urged the UN to also consider the number of innocent lives lost to drugs, before laying into the organisation in a typically expletive-laden tirade.
Mr Duterte said the UN should not worry "about the bones of criminals piling up", but instead do more on issues such as hunger, terrorism and conflict in Syria and Iraq.
"Maybe we'll just have to decide to separate from the United Nations. If you are that disrespectful, son of a whore, then I will just leave you," the president added.
The riled up leader suggested he could create a new global organisation.
"I would invite everybody. I would invite maybe China, the African (nations)," said President Duterte.
When asked about the possible repercussions of his comments, he said: "What is ... repercussions? I don't give a s*** to them."