Well, that's for several reasons.
For one, it's unlikely that the boss WILL be fired if you do that, since his manner has probably already been reported by other people or observed by management.
For another, that boss most likely will have an opportunity to retaliate by creating a critical dossier on you that can be used against you if some prospective employer in the future wants a recommendation before hiring you.
And perhaps most of all, because what you're thinking of doing is usually only good for getting yourself some satisfaction that you 'got even' with the boss, at least to some degree, before moving on. You can live without doing that.
This assumes, of course, that the boss is an unfair, egotistical, tyrant or whatever. That's what I took from the description we were given. If your question was keeping open the possibility that he or someone like this was also endangering the safety of those under his supervision or seriously violating company policy, etc, that would be different.