Mail Room Drama

Well shit, dick-lickers! I saw a fist-fight almost break out in my office, and got personally called-out as a back-stabber/bitch by the second laziest co-worker I've ever had.
I work in a mail room at an educational publishing company (right industry, wrong position, but it serves its purpose), and we see a few different types of employees roll through for longer or shorter periods of time: a few smart, over-qualified eccentric types who maybe are trying to get their foot in the door, or looking for a low-key job to work while going back to school (ahem), a few bright hard-working guys who maybe lack education, are straight up young, or have a pre-disposition for hands-on work, and a few incompetent space-case ass-backwards nutbars. This one dude, A, has been grating his fork across his plate since he got hired and basically no one likes working with him. The problem is he tries unbelievably hard to be a nice guy (socially). He weasels out of work and makes it into a joke any time you mention it, his co-workers simmer in irritation for awhile, it comes to a head and he blows up, saying why didn't you say so to my face?!
This other guy K is absolutely the back-bone of mailroom 1, and he works with A every day. K is the go-to guy for everything, and our bosses, maybe unintentionally due to passivity and laziness, maybe due to incomprehension of how to manage problem employees, put a lot of pressure on K to deal with A's BS. I'm kind of like K in mailroom 2, but my team is much more reliable, so my position is not as difficult, or as akward. That's really the problem: A is so easy-going, so unwilling to take work or anything seriously, that it's almost impossible to talk to him about pulling his weight. When shit finally boils over, he pulls this et tu Brutus act, then plays it down five minutes later.
So A has been slacking off since our assistant manager B has been on vacation. Around lunchtime K and A got into a pointless argument over some small bullshit, and for whatever reason, it escalated further and further. I started trying to calm it down but they totally ignored me. Finally they started shouting and K starts going into A in general about his sloppy work, then he brings me into it to back him up, and K got a little too personal about it, I do have to say. I wasn't prepared to go into it right there, but it was going to happen sooner or later. A gets really upset and starts fronting this gangsta bullshit, you wanna step outside, etc. I open my mouth and he calls me a two-faced backstabber, flips me off.
Meanwhile, our brand new superviser, M, in charge for the first time without the assistant superviser, is in the corner on a conference call with our big boss (the operations manager) and HR, starts leaning over, trying to figure out what's going on and calm A and K down.
She hangs up the phone, gets between the two of them and miraculously diffuses the tension right away. At this point, knowing that to throw a punch would get him fired, and knowing that A won't do it first, K zips his lip and cools down. A advances twice, still trying to look like the better man. Our super shuts him up, separates the two of them, and makes sure nothing worse is going to flare up. She's definitely green, and definitely not much for paperwork, bullshitty office protocol, etc., but girl knows how to stop a shouting match from turning into something worse.
The thing is, this is the second time it's gotten this bad. Every time A gets this heated, five minutes later he calms down and goes into super-apologetic mode, and comes up with a million semi-plausible excuses for why he doesn't like to do certain things, and he's willing to share the load more if you just ask him, blah blah blah. My whole deal is why, should I have to ask you at all, let alone over and over? Meanwhile, he still didn't pick up the mail, sort anything, process any letters, or in general pull his share of the daily weight. He cleaned up his act by a factor of one where it should be a factor of ten.
Here's the thing thing that sticks under my fingernail: after the intial deal, A and K had to step into the big boss' office to have a conference call with her. Over the phone, she chastises both of them. I'm not saying it was fine for K to call A out like that, but if the blame goes 5%/95%, is it fair to give out a 50%/50% reprimand? Fuck that shit.