He blasted Barack Obama as a "son of a whore", unleashed at a United Nations envoy as a "son of a bitch" and now a fire-laced insult targeting Australia's Julie Bishop looks certain to be next.
Philippine President Rodrigo Duterte, who has fast earned a reputation for shooting from the lip, had nothing but praise for Australia's smooth-talking foreign minister, even when asked if Australia raised concern over the delicate question of almost 8000 Filipinos killed in his so-called war on drugs.
"We never discussed human rights. They are so courteous," Mr Duterte told local media at the weekend.
"Because if you say that, if you utter those things in my presence, you'll get an insult. So what we did was to discuss transnational crimes, terrorism."
Mr Duterte's bloody crackdown on drugs crime has sparked widespread alarm about gun-happy policing amid thousands of deaths, yet nobody, not even the United States, would dare to raise human rights with him, he boasted.
"Australia? I will not pick a fight. Do not ever do that because if you can say one thing bad about me, I can say five things bad about you."
But on Monday, following Mr Duterte's denials, Ms Bishop told a somewhat different story about their meeting.
She went to Mr Duterte's hometown in the southern Philippine city of Davao promising to emphasise faith Australia' places in upholding human rights and the rule of law in democracies.
And that, Ms Bishop insists, is precisely what she did.
"During my conversation with President Duterte we discussed the country's anti-drug campaign at length," she said in a statement to Fairfax Media.
"I conveyed Australian and international concerns with respect to extra-judicial killings and spoke of the importance we attach to human rights and the rule-of-law."
More, she also raised concerns with three senior ministers and met with a a member of the local human rights commission and other advocacy groups.
It's very rare - almost unheard of - for an Australian foreign minister to so publicly contradict the leader of neighbouring country.
The conflicting accounts marks yet another sour diplomatic note to Mr Duterte's presidency, after an earlier foul-mouthed tirade directed at then US president Barack Obama resulted in Washington cancelling scheduled talks between the two.
Mr Duterte has a reputation for his brutal crackdown on drug crime during his longstanding term as mayor of Davao city, and has bristled at international criticism, pledging to deploy the army to "kill more" drugs suspects.
He had already betrayed sensitivity about Australia, lashing out at Australia's ambassador to Manilla during his campaign for the presidency, amid uproar over him joking that he should have been first in line to rape an Australian missionary.
The Turnbull government has launched a campaign for Australia to win a seat on the UN Human Rights Council in a vote to be held in October.
Human rights groups criticised Ms Bishop's decision to visit Mr Duterte in Davao, inside a zone in the Philippines where the Foreign Affairs Department also warns Australians to "reconsider your need to travel".
Elaine Pearson from Human Rights Watch Australia said the conflicting accounts of Ms Bishop's meeting with Mr Duterte show why she should have spoken publicly in Davao to condemning the killings, "so it was crystal clear what Australia's position is".
"Either her message never got through, or Duterte is deliberately distorting what she said," Ms Pearson said.
"Duterte is desperate to show he has international allies, and Bishop needs to take a strong stance in correcting Duterte's assertions so that Filipinos know where Australia stands."