There are lots of things that you can report people for in league, and all of them are because "Oh we want to make sure people aren't ruining the gameplay experience" Let me tell you a thing or two about ruining a gameplay experience.
When you're playing some ungodly difficult matchup like Yorick into renekton rammus, and your jungler is a Yi. A ruined gameplay experience is when your Yi runs top with the red buff, and after the gank happens, continues to chase the renekton into the creep wave, and then die 1v1 because I have no way to follow him nd there is a wave on my tower and we don't win an all in.
I tell him "Nice gank" and am muted by my jungler. As I proceed to absolutely dumpster the renekton, 2v1 against rammus, am 30 famr up, take teh herlad solo, take two gromps, a blue buff, the tower, mid tower, kill midlane.
Literally every possible thing I could do to win the game, never once does the yi come top or communicate, coordinate, or play with the team. He doesn't even AFK farm, he just fails ganks bottom into Vayne morgana like he has any change of getting sometihng off in that lane. Meanwhile I am 3v1 toplane, while dragon is up. I kill Rammus and Renekton, and Xerath has to back. Does Yi take the infernal drake? No he backs on his gromp with full health and mana.
"Oh well thats not a reportable offense" yeah well fuck you it should be. He refused to play the game optimally, just because he was mad. He didn't listen, didn't coordinate, didn't work together, didn't do fucking anything. Doing nothing, and actively refusing to play with or around your team is just as bad as inting. It needs to be a reportable offense, and Riot needs to ban these stupid fucks who just through games and never listen to their teamates who are winning the game, but these people are determined to lose.