My PCs know about hit points, level, and AC. Level obviously abstractly as in "I can bet that guy or I'm better than so and so." That is all level is. AC is just how hard you are to hit. Most people who fight would know that. Hit points in my definition are proportional meat so you know when you are wounded.
Level is extremely weird as an ingame element, especially if you also treat spell levels as ingame elements, but I'll leave that one alone.
"AC is just how hard you are to hit"? But isn't the fighter with 10 DEX in full plate easier to strike than the unarmoured thief with 18 DEX, or the unarmoured monk with AC 2 from special abilities? Now, of course "hit" in the technical language of D&D combat is not synonymous with "strike", but you can't explain that non-synonymy without using other notions, like "damage", that also involve game elements with no obvious ingame analogue (eg hit points).
So turning to hit points: I understand what it is to hack meat of a souvlaki skewer, slice by slice. How that metaphor is meant to extend to interpersonal combat I have no idea, however. If a PC has 16 hit points, and takes 4 hp of damage from a dagger, what does s/he know about him-/herself? How can a quarter of his/her body be missing yet s/he suffer no ill effects to her physical endeavours?
And if you don't mean literal proportionality, then the whole thing breaks down. If 16 hp of damage to that PC is the piercing of a lung, or the heart, what is 4 hp? A finger chopped off? (But you can take 4 hp more than 10 times in your life, and no matter how many times you take it you can still write and play the lute.) A scratch along the forearm? But now what has happened to proportionality? And what if the blow that kills a character is the blow that does 4 hp? No matter how badly hurt in other ways, a person is not going to die from a scratch along the forearm that, had s/he taken it in an uninjured state, would have had no adverse effect on his/her physical performance.
It seems to me that Gygax was just writing common sense when he told us that hit points, AC and the action economy were all abstractions, that do not in themselves correspond in any systematic way to ingame events, but that perform the function of regulating ingame outcomes. Plenty of RPGers didn't like that style, and hence took up games like Runequest, Rolemaster and the like. (For many years I was one of them.) As far as I can tell, the label "dissociated mechanics" is simply a pejorative label for an abstracted mechanic that the labeller, for whatever reason, doesn't enjoy.
The most "dissociated" mechanic I've actually come across in recent times is the 3E Mirror Image spell, which came under scrutiny in
this thread. Mirror image is a spell that made sense in AD&D - it represented the caster creating these confusing images within the chaos of melee. But 3E, with it's stop-motion initiative and its freedom of targeting, makes no attempt to model the chaos of melee. Which means that Mirror Image ends up making no sense if you try to treat it as modelling any ingame process.
TL;DR: I agree with [MENTION=6774827]EnglishLanguage[/MENTION] about the unhelpfulness of the label "dissociated mechanics", and am seriously puzzled by anyone who can stomach 3E Mirror Image being unable to digest DoaM (or CaGI, for that matter).