It isn’t often the president of the United States is called a derogatory term by his counterpart from a friendly nation—and cancels a meeting as a result. But that’s just what happened (paywall) after Philippines president Rodrigo Duterte deployed a derogatory slur against Barack Obama.

The Tagalog term used translates roughly to “son of a bitch” and came up yesterday (Sept. 5) after reporters asked Duterte how he’d react if Obama brought up human rights issues in relation to the widespread extrajudicial killings that Duterte has encouraged as part of his campaign against illegal drugs.

Duterte’s comments were pointed (“putang ina” in the following is the slur):

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, nobody but nobody. You must be respectful. Do not just throw questions. Putang ina I will swear at you in that forum.

More than 2,400 alleged drug criminals have been killed in the Philippines since Duterte launched the violent campaign over two months ago. Police are behind about a thousand of those, but vigilantes—encouraged by Duterte—are behind many of the rest.

Obama and Duterte were expected to meet this week in Laos, with both leaders attending a meeting of the Association of Southeast Asian Nations.

Duterte might have picked an especially bad time to insult a US president. The Philippines relies on the US providing a balance of power against China in the South China Sea, where in recent years Beijing has grown increasingly aggressive, posing a direct threat to the Philippines’ control of its own maritime resources.

Some observers have predicted that China would begin island-building at Scarborough Shoal, just off the coast of the Philippines, in the period between the G20 summit and the November elections. This week the Philippines defense ministry showed photos of about a dozen Chinese ships gathering near the shoal, with some appearing to be designed for dredging operations. It isn’t yet clear what their intent is, but building military infrastructure at the shoal would give China a strategic triangle with its other new South China Sea bases, and help it exert control in the area.

A statement from Duterte today said he regretted that his comments “came across as a personal attack on the US president.”

Obama isn’t the first prominent figure to be cussed out by Duterte over the dubious drug killings. In June, UN secretary-general Ban Ki-moon said the killings were “illegal and a breach of fundamental rights and freedoms.”

Duterte responded: “Maybe we’ll just have to decide to separate from the United Nations. If you are that disrespectful, son of a bitch, then I will just leave you.”

Even something as banal as traffic jams can spur Duterte into using swear words against prominent world figures. When a visit by Pope Francis caused congestion in Manila earlier this year, Duterte called him a ”son of a whore.”

On social media some supported Obama’s move with colorful language of their own.

“Clearly he’s a colorful guy,” Obama said (paywall) after nixing the meeting, as he wrapped up his visit to China for the G20 summit. “What I’ve instructed my team to do is to talk to their Philippine counterparts to find out: Is this in fact a time where we can have constructive, productive conversations?”

That, like the moods of the Filipino leader, would seem a difficult thing to predict.