Kim mostly answered Trump's threats to "totally destroy" North Korea if the reclusive nation attacks a U.S. ally. Trump also called Kim "Rocket Man" in his address -- a reference to the leader's proclivity for launching test missiles.
"I'd like to remind Trump to exercise prudence in selecting words and be considerate of whom he speaks to when making a speech in front of the world," Kim said. "The mentally deranged behavior of the U.S. president openly expressing on the U.N. arena the unethical will to 'totally destroy' a sovereign state, beyond the boundary of threats of regime change or overturn of social system, makes even those with normal thinking faculty lose discretion and composure."
Kim also criticized Trump's political style, comparing him to a "political layman" and a "political heretic."
"After taking office, Trump has rendered the world restless through threats and blackmail against all countries in the world," Kim said. "He is unfit to hold the prerogative of supreme command of a country, and he is surely a rogue and a gangster fond of playing with fire, rather than a politician."
Kim went on to say Trump will "pay dearly" for insulting North Korea.
"Whatever Trump may have expected, he will face results beyond his expectation," Kim said. "I will surely and definitely tame the mentally deranged U.S. dotard with fire."
A "dotard" is defined as "a person, especially an old person, exhibiting a decline in mental faculties; a weak-minded or foolish old person."