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."