Loki is, simply put, a nuisance of the highest order. Thanos loathes him. He'd been useful, yes, but he'd never bothered to calculate just how pesky the Asgardian could be. Nor how… paradoxical? Oxymoronic? Illogical? In hindsight, he can appreciate the irony of his own hatred for the Asgardian (and yes, despite Loki's claims to not be an Asgardian, the fool should know better than to think blood matters more than loyalty; Jotun by birth, Asgardian by choice). Loki is perhaps the very definition of balance.
And that irritates him like nothing else, because the picture Loki paints of balance makes no sense. Balance is order, stability, security, assurance. Loki is none of those things and yet he's the epitome of insanity mixed with grounded, realistic perception. Deception and bald-faced truth. Reckless abandonment and steely-eyed determination. Love and hatred. Loyalty and treachery. He's both an ally and an enemy at the same time. Logic both applies and doesn't apply to his motives. For all of his vaunted wisdom, Thanos cannot place the infuriating man. Everything should have at least a semblance of belonging somewhere.
Loki doesn't.
So when the fool begins to mutter some sort of vow about pledging his undying fidelity towards the titan, Thanos decides he's had enough. "Undying? You should choose your words more wisely."
(In hindsight, he's embarrassed by the accusation. The universe's self-proclaimed mischief-maker is known for his emphasis on semantic choice.)
It is no falsified illusion that he crushes. He knows this, Loki knows this, Thor seems to know this. There will be no more resurrections.
***oo***
Everything is silent now. Balanced. Perfect. Without stain or blemish, and he's reveling in it. There is a sort of peacefulness here, in a sea of grass-green hills and rich blue sky. In the midst of this revelry, two words come unbidden to his mind, seemingly out of nowhere and yet he knows they are from somewhere, but the dead don't speak. Not without permission, anyway. Not to the owner of the Soul Stone.
Not unless he wants them to.
But the trickster's never been one to play by the rules. He's never been one to act or speak on the whim of another, no matter how powerful, no matter how wise. Loki has never made sense.
Undying fidelity…
A pledge broken only through death. "You should choose your words more wisely," he'd said.
He stares, mesmerized by this planet's beauty. This peace, this balance, cannot be undone. Not by a dead man, but of course it is now that his mind conjures up the answer that the fool would have given to his accusation had he chosen to acknowledge it:
I did.
An echo of a snarky, maniacal laugh ghosts over the hills and washes over his tiny abode with the warm touch of a summer breeze. The breeze leaves a cold tingle at the base of his neck and the four words that follow are more than mere conjuring.
"The joke's on you."
"I consider experience, experience." Loki Laufeyson (Odinson)