Obama doesn't seem to be very warmly greeted anywhere these last few days at the G20 meetings - I saw one scathing report of his reception by the Chinese when they arrived ... no stairs in place for him to deplane, issues being allowed to enter the hotel where they were registered...the press corp, the staffers, everybody was getting jacked up by various officials in a very unfriendly. Some hours later there was something about a chilly meeting between him and Putin at the same conference.
If China, Duterte and Putin try to offend him, and the US btw, it is because of their lacking in civilized, diplomatic behavior. It is not acceptable for them to behave this way, and for us to accept it as warranted, is beyond ridiculous.
If you are an American and believe in civil behavior, then you cannot imagine that what these lowlife dictators think or do is acceptable. Would you think it was an okay thing to do if Hitler did it? Stalin? Mussolini? Mao? Thinking there is something warranted in what Putin, Duterte and China does is the same as thinking the undiplomatic and Cretan behavior of Stalin, Mao, and Hitler is warranted.