Undiplomatic? Yes.
Uncalculated or haphazard? No.
He is the president elected on popular vote. He needs to stay popular and, to achieve concrete results, needs to go outside the confines of political correctness.
Politicians are known to be cursing even at high level summits and at times they are caught when the mic is left open by mistake.
Duterte is a new breed of politician, like Trump, which needs to rise over the mediocrity and 'the-same-old' of traditional politics.
Trump knew that he needed to move outside the traditional Republicanism and, to this end, let so many ghosts out of the box, such as race and the fairness of the judges.
It is disturbing, yes, but, it is also like a sour medicine with long term healing effects.
PH might be regaining sovereignty right before our eyes.