Nearly every random I play, someone is raging. What's worse, even if you play well, some of these ragers live in the moment, meaning even if your score is outstanding, they still rage you if they see bad play.
Example: I was Pantheon. I became "godly" very quick, up 8/2/3 at the ~25 min mark. I was carrying my team with awesome ganks top, great gank bot, and a great gank mid. Xerath (the rager) was mid and kept questioning why I wasn't ULT'ing mid to take advantage of his stuns (as if my ULT CD is short!). I also made one bad play where I got caught in river. Xerath was quick to pick up on this and criticize. Throughout the entire team, he was on my case, even though I remained quiet. I eventually just muted him.
I find playing as Shen is the worst, because a lot of ragers assume you will save them low on health and join in on every team fight. Again, the ragers falsely assume my ULT grows on trees.
So morale of the story: Nothing you do or say will appease ragers. Your best bet is to mute them.