Kim Jong-Un called Donald Trump a "lunatic old man" recently, and Trump took offense, but not at what you would expect. No, he tweeted "Why does Kim Jong-Un insult me by calling me 'old' when I would never call him 'short and fat'?"
Earth to Donald Trump: you are 70 years of age. That's old. The insult is that he called you a lunatic. You see, a sitting US President should not actually be insane, which you very obviously are.