I agree with everything you say but I would also say that this type of response from a manager (even with the reduced third section) is a major contribution to a hostile work environment. Public ego-tripping is the antithesis of a good manager and saying "you are wrong about everything and suck at life" when you are about to fire someone is always the wrong thing no matter how frustrated you are with that person or how true you think that statment is.

I also think that using violent imagery to make a point is a bad idea in almost any context, even if clearly not ment literally. He did at least explicitly say he would not include that part if writing when on the job.