Don't think there is something as simple as insanity going on. We, and South Korea, think it is worth the effort while he is a new untested leader to try to create a North Korean spring. He is reacting to this. North Korea might continue, it might collapse under his leadership, or it might explode.
Depends on your definition of insanity? Some people are who and narcissistic are very bright.
It is simply chest beating to ensure he stays in power in his own country. No threat whatsoever.