The good old days of Season 3 Blame the Support. I'd almost begun to miss those days. NOT!
One important thing to remember, even when we have a support (or any other teammate) who is feeding and playing poorly, is that every death we have is actually due to something that we should have done differently. While it is very tempting to say that we only died because our support fed the enemy 15 kills, that's never the only reason we died. Part of playing well and making good decisions is knowing when we cannot trade with the enemy adc, when we have to back off or farm under turret, when we have to farm the krugs or try to lane swap. One of the biggest mistakes people make is getting behind after a misplay like the Brand chase, but then continuing to try and make desperate trades that they have no chance of winning.
It's really tempting to find the weakest link on the team and blame them for the loss, especially if the team is harassing you and you want to shift the focus to someone else. But that's a bit of a dangerous road to start walking. You lose some of the potential for growth as a player when you don't acknowledge personal accountability, and it can start a bit of a flame war if you start to argue with your teammates about it in chat.