Why were Erin and Andy not fired after they flipped out on Nellie/Robert?

Question

In The Office S04E12, Stanley flipped out on Michael during a meeting:

Michael: An urban, yeah, Stanley? You wanna help us out with that? ... Stanley, earth to Stanley....

Stanley: Not me.

Michael: Yes you. Come on, Stanley, put your little game down and join the group.

Stanley: No.

Michael: Stanley, we're havin a little...

Stanley: Leave me alone, dammit.

Michael: We're having a little brainstorm session...

Stanley: DID I STUTTER?

Michael: ...Good, this is good. I'm going to grab a glass of water.

On this exchange, Toby was very keen on Michael doing something, as a subordinate was clearly insubordinate. He even suggested firing him.

A few years after, Nellie replaces Andy as manager while he is away, and due to this, Andy and his girlfriend Erin have a row with Nellie and the CEO, Robert. One particular time:

Nellie: Erin, on phone memos you're writing the date American style. Month, day, year. I prefer it day, month, year. Small, bigger, biggest. Oh, sexual innuendo. Not intentional.

Erin: Shut up. Shut up! I am sick of your dumb opinions. And if you don't like the way that I take phone messages, here! [throws phone] Take 'em yourself!

Andy: Oh, and another thing! Our sex life is none of your businesses!

Erin: And Andy is the manager, not Nellie!

Andy: Stop protecting me! I'm a man. I can protect myself! This is misdirected anger and I'm sorry! I don't mean to lash out at you! There's a lot coming up right now, all at once! [into phone] Dad go to hell, I'm taller than you!

Nellie: Okay, just calm down.

Andy: You are not the manager. I earned that job. I was personally chosen after Robert was chosen and quit.

Robert: Andy, why don't you just take a seat?

Andy: Why don't you take a seat, you idiot? [throws chair]

It was a pretty ugly exchange considering two employees went off on the company CEO and the Branch Manager.

The question is, if the HR was keen on suggesting to fire an employee after they spoke rudely to their manager, where was HR this time when the employees not only threw stuff at the bosses but also shouted crudely? Even called the CEO an idiot. Why were they still spared? How were they not fired right away?

I mean, Robert never seemed a forgiving guy. How could he let go of Andy shouting at him and throwing a chair at him in front of the whole office?

Answer 1

Robert was a very enigmatic character who valued confidence over capability (clearly, as Andy was far from the sharpest tool in the shed). I would say that he was not threatened by Andy's outburst and likely kept the incident as leverage in his back-pocket to use later (against Andy) if the situation ever suited him.

I didn't address HR in my answer as it wasn't every really a very important part of the series. Toby was an ineffective HR manager, soft-spoken, mousy and sometimes petty but never really good at his job. With his crush on Pam that he never acted on, he was portrayed as a passive-aggressive wallflower who never really contributed much to the show.