Most responses are hyperbole. Undefined behavior likely doesn't include making up new code; its not certain where you will end up, but someplace in existing code is a certainty.
Even excluding obvious fantasy like nasal demons, and real but unusual cases like starting nethack, there are completely mundane things that are reasonably common in real compilers but that don't go "someplace in existing code", like aborting on integer overflow, or crashing when you access a bad pointer.
