How does one earn a ban?

So, I'm aware that Riot shows a bit of leniency towards people who rage or look like they're feeding on the surface, giving people the benefit of the doubt that they're just having a bad game/bad day. People who do these things only on rare occasions rarely get banned. I'm aware of this, I understand this, that's all fine.

But what about people who intentionally troll? Who say outright in pre-game chat that they're going to troll and want us to lose, and then whose behaviour in-game matches their words? Is punishment handed out more liberally in these cases? I just finished a game with a rather toxic player who did just that, one of the most toxic I've ever seen in the many years I've played, and I'm really hoping he gets a ban as punishment for his atrocious behaviour, rather than being passed over should it be something that he doesn't participate in frequently.