TLDR: If you had the opportunity to meet up with your recent teammates/opponents IRL and have lunch, would you refuse and hold the grudge against them because they costed you your promos?
Imagine this scenario:
The new school/university year just started and you got to meet a lot of new people and make some new friends. As the days go by, you all share about each other's interests, and the common ground between you all is video games (not just League of Legends). Here's the kicker: in this scenario, you've played with/against **all** of these people before in the past year or more.
How many of these new friends have you cussed out in a past time? How many have you told to kill themselves? How many have you wished illness upon them and their family because they stole your blue/red buff?_
Just because they're represented as a champion in game **does not** mean that they're any less of a human being. Believe it or not, they all have issues in life just like you do too. Sure, there are many trolls out there that find joy in intentionally ruining the fun in the game.
There's also people that cut you off while you're driving to work/school. The majority of those people also have urgent matters to attend to.
We're all human, we all make mistakes, and we're all reading this from a screen somewhere in the world. And in the extremely rare event I had the opportunity to meet you IRL, I'd buy you a coffee/beer/RP because you're already a pretty awesome person.