The two presidents would be "wallowing in the mud like pigs" if Barack Obama lectured him on human rights, Duterte told reporters on Monday.
The outspoken Filipino leader was answering a question on the US stance towards the Filipino drug war, an issue likely to be raised at a scheduled meeting in Laos on Tuesday.
"You must be respectful," Duterte said, pointing out he would not take orders from the US. "Son of a whore, I will curse you in that forum."
"I don't give a shit about anybody observing my behavior," he added.
'Plenty will be killed'
Duterte was elected earlier this year after pledging to beat back the drug epidemic in the Philippines. Some 2,400 suspected drug dealers and users have been killed by police and vigilantes since he claimed office on June 30. The president himself has encouraged the killings.
"More people will be killed, plenty will be killed until the last pusher is out of the streets. Until the (last) drug manufacturer is killed, we will continue and I will continue," he said on Monday.
The ongoing crackdown has sparked much international criticism, but Duterte repeatedly dismissed it, often using vulgar language. He has also cursed the pope and the UN General Secretary Ban Ki-moon.
In his Monday remarks, Duterte also brought up US colonization of the Philippines in the early 20th century, accusing Washington of crimes against the country's Muslim minority.
"Who is he to confront me?" Duterte said of Obama.
"I am a president of a sovereign state and we have long ceased to be a colony. I do not have any master except the Filipino people," he added.
Obama calls for 'due process'
Soon after Duterte's press conference, Obama said his aides were assessing if a constructive meeting in Laos was still possible.
"Clearly he's a colorful guy," Obama told reporters in the Chinese city of Hangzhou, at the end of a G20 summit.
"Obviously the Filipino people are some of our closest friends and allies," he said, adding that "fighting narco-trafficking is tough."
"But we will always assert the need to have due process and to have that fight against drugs in a way that is consistent with international norms," he said. "Undoubtedly, if and when we have a meeting, this is something that's going to be brought up."
Obama and Duterte were due to meet at the sidelines of the Association of Southeast Asian Nations (ASEAN) summit in Laos, scheduled to start tomorrow.
dj/rc (AFP, AP, Reuters, dpa)