Maybe you shouldn't enter a ranked game?
It is very frustrating to have a teammate who can't even play. I personally don't blame Riot or their services, I've played the game for 3 years and have never been disconnected. If you start feeding, don't blame it on lag then sit at fountain all game, spamming surrender, move a bit then claim you can't play if you are lagging and can't play. How about not ruining everybody's game and just not play ranked?
It is rarely "computer". It is internet and internet connection is not something you can absolutely controll. Someone who never d.c might d.c one game.
It's great that you've not had any issues for three years and until the last few days, I haven't had any problems either. But the fact remains that there is some sort of connection problem going on, and it's affecting a lot of players. Seriously, go look at the Help & Support board, it's nuts.
However, I do agree with you; it's pretty clear to see there is a lag/disconnection/login issue of some kind, so playing a ranked game** knowing **that you'll probably disconnect miiiight not be the best idea.
I've been steering clear of any PVP matches until things get cleared up. Sorry to hear someone joined your game like that. :(
