*whispers* Viktor never once says anything mean or belittling to Jayce after they become partners. Not one insulting "you" statement, not one disagreement where he doesn't remained focused on the point of contention. He never makes ad hominem attacks, he never insults Jayce's appearance or intelligence.
Literally the single meanest thing he says to Jayce that could be considered a "you" statement is "Your mind has become rigid." Basically, he's saying that Jayce has suffered so much recently that it's closed his mind to broader intellectual possibilities like, that is barely an insult, and clearly Viktor just means it as a statement of fact, if not a challenge for Jayce to joyously consider possibilities again. And by the way? That statement is when Viktor is in his full his villain arc. It's remarkable because it's the only time he's pointed out a perceived flaw in Jayce since the night when he questioned if Jayce signed his notes out of being egotistical.
From the moment Jayce told Viktor about how beautiful magic could be, arguably once Jayce became a person to Viktor rather than a subject of academic discipline or skepticism, Viktor has not once leveled a personal attack against him as a person. Not even during the fight on the bridge. Not even when he called Jayce's Councilor work a waste of our time. Not even when Jayce was considering making Hextech weapons, Viktor still remained focused on the substance of the argument, expressed incredulity, anger, even disgust that Jayce would consider making weapons, but he never said it was because Jayce was stupid or privileged or blind. He pointed out specifically that he knew Jayce felt trapped by the decision, he knew Jayce was being manipulated, and then, in a very pointed manner, Viktor reminded Jayce that there's always a choice, challenging Jayce to stand firm and do what was right.
Even when they parted ways in 2.02, Viktor didn't say there was anything wrong with Jayce. He just said their paths had diverged, again not saying anything was wrong with Jayce, or even his choices, but rather that they're two different people who had stayed together longer than their diverging goals normally would have allowed because of the affection they held for each other.
I don't know, I get why people write Viktor as catty or mean or dismissive of Jayce. There's definitely some quotes from the day they met, before they become partners, that lend to the idea that Viktor can be quite dry and sharp with others. And conflict is the stuff of good fiction so again, totally get putting some conflict between him and Jayce in fic.
But I also think there's a tendency in derivative works like fic to Flanderize the characters, or worse, put them into narrow archetype boxes that are vastly different from their more interesting and nuanced canon selves.
How many times have we seen a wiggly man/straight man or blue vs. red personality partnership duo? How often have we seen those partners not be able to fucking stand each other, who are bickering all the time, who are snide or backtalk, or are perpetually sarcastic?
It's so common that I get why people see it with Jayce and Viktor but that's why it's so damn fascinating to me that they aren't like that.
Jayce and Viktor don't suffer each other unwillingly at any point, even when they're having a goddamn flying superhero fight in the final episode they're talking about how they're happy to see each other and praying that the other will please step away from this destructive path! They don't want to hurt each other, even verbally!
During the years of their partnership, they're constantly delighted by the other's presence, they are instantly comfortable together and never have a bad word to say to or about each other. They actually don't bicker! When they have disagreements, they stay entirely focused on the point of the disagreement and they never dip into personal attacks of any kind.
Even the tone of the time Jayce yells at him on the bridge, arguably their most acrimonious moment in the whole first season, isn't an actual argument, no more than a parent yelling at their child for running into traffic is an argument. Jayce says awful things but it's clear his anger comes from fear for Viktor and for their precarious situation. And it's clear this is a deeply unusual moment for both of them, Viktor is taken aback at how unusual it is, Jayce once called out backs down immediately, arguably because it's so unnatural for them to fight at all that it takes the wind out of the sails of Jayce's anger instantly when he realizes he's crossed a line.
No one can drag a bad word about Viktor out of Jayce, and vice versa! When Singed implies that Viktor might lose loved ones over his choices, Viktor immediately (and correctly!) states that Jayce will understand.
They are rigorously protective of one another too. Arguably all the times Viktor excludes Jayce from his Hexcore experiments in S1 is to protect him from his reckless and likely illegal experiments (as well as not wanting Jayce to stop him and wanting to live, but it can be many things). Jayce constantly cites Viktor as his partner and constantly reiterates that Viktor is his priority in life, that saving Viktor comes first. Jayce overthrows the goddamn founder of the city in order to protect Viktor!
Jayce's love for Viktor is so extreme that literally in S2, the only person who can convince Jayce to hurt Viktor, after seeing the post-apocalyptic Hell of a future that is caused by him, is Viktor himself. Jayce doesn't even get mad at Viktor after he learns Viktor is the cause of what he saw! He is instead desperate to get back, to avert the damage caused by their joint work in Hextech, and saved Viktor from the fate worse than death that is Mage Viktor's total isolation in the aftermath. And every step of the way, even knowing what he knows it's clear he's in agony at the thought of having to raise a hand to Viktor at all.
Now of course I'm getting into just how insane their love for one another gets in S2, but I just feel so baffled sometimes reading fic where Viktor is constantly undercutting, insulting, or belittling Jayce every which way. He never once does that after the partnership begins. And it makes me so insane because we have so many partnerships in media that do devolve into sarcasm, cattiness, and backbiting but Jayce and Viktor aren't one of them and that's really really fucking interesting and worthy of exploration I think.