Having an issue with your teammate?
No problem! Just list the things they're doing, in a whiny way. Doesn't matter if they made the right move, or a huge play, or they were just cleaning up your mistakes, as long as you sound whiny it'll be totally insulting and justified. And they're getting kills? Well they're bad because one game you were twice as fed on that champ, in a bot game.
And if that fails, just cry about their build! Most of the time your team won't play a given champ enough to know what they build, so if you start crying about Urgot being a troll for going AP when he buys tear, that'll work. And if it's a situational build, even better! Who cares if the enemy team has 4 mages and a Corki, your tanky champ didn't build that much MR in that LCS game you saw.