Mafiafell (SOLYGBM) Analysis spoilers for 125-130...
A/N: it HAS been a while since i've done this but GOODNESS! I could NOT keep containing this I was going crazy.
Starting off strong, I think one of the reasons Sans shows feelings of annoyance and irritation towards Papyrus whenever he talks to him isn't just because he's loud, mostly because he's gotten used to that by now. It's because Papyrus reminds him of Wingdings through the way he speaks, his mannerisms, and just his general behavior.
Not exactly like Wingdings, but the fact that Papyrus is always scolding him, and while his loud booming voice is supposed to separate him from his older brother, it only makes Sans more annoyed and irritated. Papyrus is always watching him and keeping an eye on him, just like Wingdings did, treating him like some child that needs to be watched 24/7 so he doesn't do something stupid. Papyrus really looked up to Wingdings, not having many other choices for role models considering he never really knew his mother, and barely knew his father. It was either Sans or Wingdings, so he picked up a lot of his mannerisms from him.
Which Sans wasn't exactly happy about.
Knowing how strained his relationship with Wingdings is, because of what Wingdings was like towards him and still is to some extent, and what he did whenever Sans behaved "incorrectly" or did things Wingdings found distasteful. Like his drinking habit. Wingdings used to put a shock collar on Sans to fix his behavior, and while it did make Sans control his drinking to some extent, he still had plenty of occasions where Papyrus had to drag him home after staying out late drinking. Because of that, the similarities in the way Papyrus scolds him and acts around him feel far too familiar. It reminds him a lot of how Wingdings used to be.
While he knows Wingdings wouldn't react the exact same way now as he did when Sans was younger and his drinking and behavior were far worse, Papyrus' loud voice, constant checking up on him, and the way he acts whenever these topics come up really doesn't help. To Sans, Papyrus is almost a copy of his older brother. The only major difference is his voice. At this point, that's really the only thing Sans can use to separate him from Wingdings. He doesn't show it, but it does make him uncomfortable. And because of the way Sans is, that discomfort usually turns into annoyance and irritated anger.
In my headcanon, whenever Sans and Papyrus fought a lot when they were younger, it was because Sans got fed up with Papyrus' constant scolding and behavior. At the time, Wingdings was still doing the same things and handling Sans in the same way because of his drinking and behavior, which only made everything worse. Then Papyrus started joining in on the lectures and criticism. That really wasn't helping, and it caused Sans to lash out at Papyrus, leading to the two of them fighting a lot.
Now that Sans has become less of a heavy drinker, and Wingdings has mostly backed off when it comes to his behavior, he mainly gets irritated by Papyrus constantly climbing onto his back like a leech, always asking why he's late, analyzing him after nights out, and generally acting the same way Wingdings used to. Sans has also gotten much better at controlling his anger, so it's far rarer for him to lash out because of Papyrus' actions. He learned from a very young age that letting his anger get the better of him never led to anything good, so he's become much better at keeping it under control.
There are still times when he gets close to snapping, though. Papyrus always looked up to Wingdings as a role model. Growing up, Wingdings was one of the only parental figures he had. (If we could call Wingdings a prental figure at all to begin with.)
So it was only natural for him to look up to him and pick up some of his habits and ways of doing things. Even after Wingdings eased up on constantly checking Sans' behavior and became less rough with him, Papyrus had already learned a lot from watching him.
And his mindset too, which was the reason why he doesn't like Sans' rejection and objection and getting angry beacuse of what he's doing. He only wants the best for his brother, he just doesn't understand it. Just like how Wingdings said it.
As a child, most of what he saw was Wingdings keeping an eye on Sans, scolding him, and trying to correct his behavior, so without really realizing it, Papyrus started doing many of the same things himself.
Not knowing any better because of the environment he grew up in and the way Wingdings raised them, Papyrus also saw how often Sans' anger got the better of him, and how Wingdings would respond by hitting him or fighting with him. So whenever Sans got angry at Papyrus for his scolding or behavior,and lashed out at him,Papyrus would immediately fight back.
In his mind, thats how those situations were needed to be handled, because that's what he had grown up watching. And seen its affectiveness. Its just Sans that cant see that what he and Wingdings are trying to do for him is to help him.
