What to do when someone decides they "don't care" in a game?

This is seriously starting to piss me off, it's like a group project in which one guy keeps destroying your progress because "Lol I don't care". Newsflash, fuckwit. There's four other players on your team, four players that do care.

I don't know about everyone else, but I don't particularly enjoy sitting there for 40 minutes working my ass off only to have it thrown away by one person's lack of interest. But what can we do against it? If someone decides they "don't care" the game is over instantly, you're playing 4v6. But you can't report these people because - as far as I know - there's nothing in the Summoner's Code that disallows this behaviour.

It's a grey zone that, in my opinion, needs to be adressed in a competitive game like LoL.