Before Yasuo came out, the champ who had this issue was Riven. She was the most likely champion in the game to ragequit after her first death for over a year, if I recall. Riven players are still like this to an extent... but Yasuo has far eclipsed her as having the most obnoxious players in the game.
Yasuo seems to appeal to the teenage edgelords of the world... all wanting to be the anime badass supercarry that puts the team on his back. All arrogant as hell and convinced they're the best player in the game but that their team is holding them back.
In Riven's case she fed the same kind of ego. Her kit was manaless and spammy, and she was encouraged to go in yolo hard early because her level 2 was one of the strongest in the game and she was INSANELY snowbally if she got an early kill on you. So she was played by people who wanted to just faceroll on you over and over again because that was a valid strategy for her at the lower ranks where it was pretty likely to work. At higher Elos people like Boxbox made outrageously difficult technical plays with her, making the average Riven player twice as arrogant and obnoxious because she was "mechanically demanding"... even though most of them didn't do any of the animation canceling or high level tricks she had. Then of course, Riven's character is a very weeb-bait brooding anime waifu to bring in the angsty teen edgelord crowd and the neckbeards and... boom. You got a champ with one of the most obnoxious playerbases in the game.
Then enter Yasuo... and he ticks almost every single box Riven did and then some. He's a broody anime badass for all the teenage edgelords (Seriously, this mofo has NOTHING but edgelord skins out of a 14 year old boy's bad fanfics). He's a spammy, manaless champion that isn't that hard to play but IS hard to play well. Every Yas thinks they're pro because of how "hard" he is to play... when he's got no resource management to worry about, his kit is VERY powerful and unlike old Riven he scales really well... so even when they yolo in and die four or five times early they're still assured of being relevant if the game lasts long enough.... which they will tned write off as skill and further boost their egos. Add in that a lot of people feel validated by "haters" and Yasuo has a lot of hate... and you can see why so many Yas players think so highly of themselves. To further the problem, Yasuo's ult is very strong but very team-reliant... encouraging the belief that Yasuo's TEAM failed him by not picking or playing to better enable him. After all, he's the real hero and the other players are just his anime sidekicks, here to watch him 1v9.
Save yourself some stress and just ban him every game. He's not even OP or anything... but it's generally just not worth having him in the game on either team... because it's 90% likely that the person playing him is going to be some flavor of toxic asshole. Save yourself the stress and just ban the mofo... or at LEAST mute anyone playing him the second the game starts.
