@modrobert @th It never was.
What you mean was a hard lockup, most often related to system extensions. Basically the equivalent to a Bluescreen or Kernel Panic. This showed a dialogue box with a bomb icon and a restart button. It was a thing in classic Mac OS, meaning before Mac OS X was released over 20 years ago.
@modrobert Can you recall anything about it? Like the platform, OS, maybe a rough version number?