sport, he is already setting down in his mind an agenda for revenge. this is a man who never forgets a slight. reporter: those who have chronicled his life say trump is obsessed with the idea of being laughed at, a line he often repeats. the world is laughing at us. the world is laughing at the stupidity of what we have done with immigration. we re the laughing stock of the world. the world is laughing at us. reporter: at some moments today in the u.n. general assembly, the world was laughing, or at least smirking at president trump as these german diplomats did. biographer say for donald trump being laughed at strikes at certain insecurities which go back a long way. for his entire life donald trump has been worried about being humiliated himself. he s a person who s motivated by the desire to escape being shamed. he s always worried that people are laughing at him.