It makes sense for a national leader not to meet with someone who calls him names. It undermines national prestige because he represents a country.
But it doesn't bother Obama when Iran's leader calls for "Death to America". It only bothers him when Philippine President Rodrigo Duterte refers to Obama as a "son of a whore".
An actual American leader should hold the honor of his nation at least as highly as his own honor. It goes without saying that Obama does not. That he cares nothing for America's honor, but a great deal for his own. That he will pursue diplomatic relations with countries that abuse America, but walk away in a huff when an ally that insults him personally.
And there also lies the discrepancy.
Philippine President Rodrigo Duterte is under fire by the left because he's fighting drug dealers while Obama frees them from prison. Setting aside his own character and style, this is the core reason why the left hates this, It's not his style. If he were pulling the same shtick while freeing drug leaders, the left would love him, just as they adored Hugo Chavez and certain Latin American leaders whose language and style leave much to be desired.
The perfect example is Israel's Netanyahu who is unfailingly polite and civil, whose rhetoric is high minded, and yet gets treated by Obama, the media and the rest of the left as if he had called Obama, a son of a whore.
Obama does not have a problem with enemies who threaten America... and on some occasions berate him personally. He has a problem with allies whom the left hates, no matter how polite they are.
This isn't really about language. It's about the left. It's about the fact that America is now run by people who have no allegiance to her. Obama's mother was the first in the family to betray her country. Obama has followed dutifully in her footsteps.