The favorable reffing for them in their first season was real and the team was low-key dirty but everyone looked the other way because it was a feel good story: especially in light of the shooting heading into the season. Now, I wish the Kings were low-key dirty so I'm not against that style of play but you aren't going to like that team when they are a division rival. They then moved past low-key and straight into known asshole territory which, again, I wish the Kings were.
That's a reason for hating the team. My reason for wanting them to lose every game is the fan base for two reasons:
1 - Rational or not, I'm not happy for any new fan base that just gets to experience sustained success right off the hop. f*** them. This fan base is the equivalent of the Avs from the mid-90s through early '00s. They were insufferable as well and, funny enough, beat the Kings in the playoffs too in an era much like the current one where going to the playoffs wasn't automatic for the Kings. There is no rule saying a fan base has to suffer before winning but I believe in it as a fan of a team that took 40 years to win a Cup and took 25+ just to make a SCF appearance.
2 - While the point above might be irrational, my hatred of the Vegas fan base is rational and rooted in my personal interactions with them at both Kings games and a game in Vegas. Having had seats for 20 seasons, I've run through the insufferable Avs, Wings, Pens and Hawks fans. Pittsburgh isn't here often so it wasn't that bad and the Kings were good while the Hawks bandwagon was going so at least there was somewhat of an offset there. While the Avs and Wings were on top though, the Kings sucked and these two fan bases were complete dicks. At least Detroit mostly sucked for its entire existence until the 90s but the Avs were a bunch of entitled pricks: the Vegas fan base has followed in those footsteps and been even worse. While I stopped going to games as often during the 2019 and 2020 seasons, I specifically avoided going to the games against Vegas as I don't need to be arrested at my age for getting into an altercation at a sporting event.
The top hockey moment for me since Vegas entered the league was the phantom major call against San Jose and the subsequent meltdown by Vegas. That meant that a Sharks highlight is my favorite hockey moment since the 2018 season. I hate this team more than any other one in the league and it isn't even remotely close and it is almost completely due to their fans. The current final four is a complete nightmare as the Islanders are the only ones I want to see win it and a Tampa/Vegas final is the absolute worst case scenario. I hate Montreal too but I'll be rooting for the upset and hope that the clinching game is in Vegas so their fans can see them lose in person.