League of Children.
Unfortunately, this game seems to attract a very toxic community. The best you can do is ignore them and report them after the game and hope that Riot will take action against them. If they make it a trend, eventually they will be punished for it.
Usually you'll find the worst players are the most vocal. They're probably more frustrated at how poorly they were doing and wanted to take it out on everyone else, because personal responsibility is a foreign concept to them. Who cares? Nothing you can do about it, no reason to let them get under your skin because it'll only drag you down and put you on their level.