Why be an unprovoked jerk?

Too often, nearly every game or every other game, I see someone who's a huge dick, for no reason, literally! And by this I mean; they're not toxic because they're losing, they're just, deciding to be a dick. First example would be in one match I had earlier today, This Akali was winning lane, no one had said anything, at all, but all she ever said anytime she got a kill was "EZ" or she would laugh at her opponent and insult them. But whenever she was killed, the one who killed her was a "tryhard" or lucky.

Another form of unprovoked assholery is being the guy who always feels the need to call out any tiny mistake of the enemy team, without them first talking shit to you. People who say shit like "Nice flash, heim" or shit like "nice try kid" or whatever the hell.

I just need to understand the mentality, so I'm asking the assholes of this game, why? Why do you feel the need to be a dick, toxic, and just overall unlikable, even when unprovoked? And "It's a competitive game" isn't acceptable. I play this competitive game, and I still act like a decent human. Many of my friends are non-toxic as well. I've met many many many people, my team and enemy team alike, who are perfectly capable of being sensible humans. So, why be such a dick even when unprovoked?