The last I just played was a nightmare. We had afk Blitz and Tahm who fed and then would swallow you and give to the enemy team. I mean that is just insane and has no place in the game. So, what's you guys worse feeding story, either of you doing it or a teammate doing it?
Had a game where out midlaner never loaded and our jungler fed early kills to the jungler and midlaner. Top kept getting ganked and died multiple times and eventually go mad and AFK'd. I was a support Nautilus and finished with a 1-0-2 score. My adc and I stayed really positive and the enemy team were pretty understanding about the issue. The loss sucked but it happens and thankfully doesn't happen often.
i had a ranked game with a support sona who kept on auto attacking. even after i pleaded with her to stop she kept doing it and messing with my cs. she never bought sighstone didn't ward at all and bought a manamune. I would have preferred if she had gone afk at the start at least then i'd have a level advantage.
Another game a few years ago i had a mid 
who fed the enemy xerath so much that he decided to intentionally feed. He just walked right down bot lane for anyone to kill him. This would be your run of the mill "intentional feeders ruin game" but, we were actually winning, or at least not dying. Every team fight after he started to walk into the enemy nexus tilted in our favor. but while we did technically win those team fights it was always at such a great cost that we couldn't capitalize on them afterwards. After, i kid you not, 20 minutes of this, who's 2 items behind the enemy xerath, who's five level under the rest of the team, realized that we might be able to win and started to actualy help out with the rest of the team fights.
.....
we lost the very next team fight. This time it wasn't his fault. The pressure had finally gotten to me and i was caught out near dragon, but I do take pride in the fact that we held on long enough for a intentional feeder to reform his ways.
