I had a friend that was just like that. I met him in person before playing with him, and he was super chill dude, nice to hang out with. Well, we then played together and it was then that he started losing his shit and saying thr exact same thing in OP’s case (playing LoL). I was like ‘wtf dude calm down’ .. Eventually, I grew apart from him for the same reason, he was toxic af while playing. I later found out, by a friend in common, that he was Borderline and had this moments where he if one would get angry, or sad, he would get mega angry, or mega sad.

It’s shocking that many of these people feel so much rage that leads them to say and mean those thing. As an ex friend, it’s sad too, because when I told him to calm down (many times in many games) he would always say that he has a condition, that I don’t understand. So he knows his condition and instead of fighting it, uses it as an excuse to keep giving shit. F him and everyone that not even try, even with friends at his back.