The end of game report card can check pre-game chat, all you need to do is specify in the notes section.
if you are no longer in a game with them, submit a support ticket
Send a report through the support ticket function on the website
So do we all. Riot promised it for us on season 1, but Riot is well known for keeping their promises to victims.
This has been brought up numerous times and while I do think it would help, the way I see it just seems like an easy way to dodge. When you think if stuff like this you also not only need to see the good it does but also the bad.
If you can report this basically means you want a free pass to end the game with no fault. What's stopping someone from a random (false) reports? Or asking for reports because of "troll" picks? There is just way too much abuse this can cause.