No directly related to the intentional behaviour of players bit something that is causing me a lot of grief recently.
I have lost more games than someone should simply because someone from team has "lag" problems with really high ping. Inversely, I have also won quite a few games because enemy team is 4v5. Of course enemy team don't always reveal that they have 1 afk due to lag but I can assume this isn't an uncommon cause considering how often it happens in my own team.
Naturally it pisses you off more when the lagger is in your own team rather than enemies. I feel like there should be something implemented to address this issue. Perhaps a constant ping test running in the client background and champion select, which denies players from connecting in the game (and thus allows for a remake without penalising the lagger?) if their ping is higher than a certain threshold.