I sometime am, and will continue to be that guy.

At least partly because it's the right way to handle post mortems, but partly because coworker X is only a symptom of the problem - and the underlying problem here is a manager who hasn't got a process in place to ensure Friday afternoon rush fixes on production don't happen. That's a process problem which is neither your nor coworker X's fault. That's my fault. Sorry...

(And maybe coworker X is a serial offender for this type of fuckup. Also my fault.)

I wouldn't rush to blame you if you were my manager. It's not the manager's job to breathe down everyone's neck -- they have to make sure to foster the right culture (like don't push potentially breaking changes to production at Friday afternoon) and ensure that the people hired are actually able and motivated.

From then on though, all bets should be off. Maybe the guy/girl had an awful day and is otherwise excellent. Maybe they felt pressured due to miscommunication (or a coworker being an ass and they took it personally and figured they'll speed through the task), or maybe they simply were novice in that particular problem or technology.

None of that would be your fault.

"He/she knows they screwed up. No need to pour salt on the wound."

Which is completely fair. But I've also seen fairly clueless people in responsible positions screwing up again and again and again and never being called out -- and those scenarios are not okay.