Let's not trivialize verbal abuse by calling it hurt feelings.
I'm not saying this level of seriousness is what happened here, but you exaggerate in the other direction.
What an employee says about their boss generally has zero implications on their career and lives, so long as it does not outright accuse them of a crime. When's the last time someone called you to provide a reference on your boss? I thought so.
In turn, what a boss says about their employees can be entirely career-ending and therefore life-altering, even if said in jest or later retracted. A higher standard exists precisely because the stakes are so much higher.
Even if you know the lines aren't blurred, if you perceive others acting as though it's up for debate, you're more likely to consider bad-faith appeals to the subjectivity of abuse as perhaps being in good faith. Few among us are philosophers capable of reasoning everything through from first principles, all the time, so these things matter.
Tone and body language are like 80%+ of in-person, verbal communication.
We need to be very careful to, as I mentioned, not “abuse” the term abuse to the point where it becomes meaningless. If everything is abuse, nothing is abuse, and we need to invent a new term.
We don't take ourselves too seriously, and find people who do take themselves seriously worthy of some extra piss taking to bring them down a peg.
(Oh, and rm -rf'ing your HD *would* land you in very serious legal trouble. It is a criminal act under the Computer Misuse Act 1990. And rightly so.)
As does some of the conduct that may lead to the counterparty calling you names in the heat of the moment.
You'll see plenty of it here on HN - some commenters are great at just staying within the guidelines while pushing others over the edge in frustration.
It's similar to probationary periods - you'll see a few people fired right at the three month mark but it's usually more of a case of giving that employee grace for the probationary period rather than accelerating a firing that'd happen later.
Persuading the tax man that the cleaners who in effect are your direct employees are "freelance" somehow and so you shouldn't have to pay the tax. Or claiming that the labourers you hired don't get paid from 0830 because they aren't "really" working until 0900 even though they're in a company minibus being driven to the worksite and this is the only way they could get there.
Neither of those things is legal here but both of them might happen and will only sometimes get reported and those responsible will get at worst a fine. If you tried anything like this shit with Sam who has a penthouse office in the City he'll summon a swarm of employment lawyers and ruin your life, but because Mateusz who cleans the toilets has dubious immigration status and he's behind on his rent he's probably not going to make a fuss when you steal from him this way. This sucks.
The problems are always at the very bottom. People who are closest to the poverty line, most easily replaceable, least easily able to organize and demand better and also most separated from those who have more freedom to demand change. One important angle unions think about is schemes to separate these low wages workers from colleagues who would be able to advocate for improvements. If the guy cleaning the toilets doesn't legally work for the same company as the guy who uses them, suddenly the question of whether "cleaning toilets" pays a living wage isn't a matter of employee solidarity...
Edited: Swapped Manhattan for the City (of London) because the topic is specifically UK employment
"Section 94 does not apply to the dismissal of an employee unless he has been continuously employed for a period of not less than two years ending with the effective date of termination"
Section 94 is the name of a section of the current law regarding the general idea of like, employing people, and that section says you can't unfairly dismiss them, so this sub-sub clause says that only applies after two years.
Edited to add: This stuff is easier to find in the UK because although it's legalese, the Westminster Parliament is obliged by its own rules to name laws after what they do, this is an employment law so I searched for "Employment". In the US it might be called the NICEHAT Act or Jim Smith's Law or some other useless nonsense because they have no such rule.