*Twice* today

Twice today, I have had an intentional feeder on my team. The first time it was a Yi jungle who started raging in chat about something or another early game, so my entire team muted him. He then proceeded to feed to show his pent-up angst that he was unable to express through typing his vitriolic comments. I shrugged it off, accepted it as a fluke loss (an annoying one, nonetheless), and moved on. The second one, though. The second one.
(fire for emphasis on how painful it was)

We get in game and I'm playing Vayne adc. Thresh and I are up against a Blitz/Jinx bot lane, which is rough for me as Vayne in early game. Due to a few ganks from Evelynn and bad positioning on my part, I go 0/5 in laning phase. It was bad, yes. I'm not a super-amazing Vayne player. I'm getting better with her. But I didn't give up. I didn't throw up my hands and say welp, there goes the game. And everyone on my team has the same mentality, EXCEPT for this Riven top lane. She gets mad and starts raging in chat (because she was ahead 2/0 on Volibear and that obviously means she's the greatest Riven player in the world) but I don't respond and instead focus on the game. We have a few good teamfights and I get a triple and a double. Riven, still mad at everyone, puts up a surrender vote at 20 minutes when we're only behind by 4 kills. When everyone but her votes against surrendering, she then proceeds to sell all of her items and run into the enemy team repeatedly. Her reasoning is summarized in this sentence "we already lost I'm just speeding things up haha you guys all suck 1v1 me l8er I will beat u nub." But we hadn't lost. At least, we hadn't until Riven began with this defeatist mentality. She starts saying how much better she is than anyone on her team in all chat, especially calling me out. "She thinks she's better than me because she got fed a few kills." "She can't even 1v1 me." (well, obviously not, you're on my team). But I never once said I was better than her. Someone from the other team did, though. He/she said "Well, she is better than you because she didn't give up." And I don't think you ever should give up.

Our Karma was in her promos and I think what she said kind of summed up my feelings about this:

I'm so glad I got demoted I'm so glad that happened I'm so glad Riven is solely responsible for my rank I'm so glad I can't control this

The thing is, I'm sure that Riven has done this before. I'm sure that Yi from the earlier game has done this before. And what I don't understand is why in the world are those people still playing this game and not banned? One in a day I could maybe see as a fluke, but two? In ranked? On the same day? If that doesn't show that Riot's current system for dealing with feeders isn't screwed up, I don't know what does.