It should not take me saying "I got autofilled to this role" for you to stop flaming
So yes - I got autofilled twice to top lane (hardly ever play it). The second time I forgot to say I was autofilled. Picked kayle - they then picked riven.
It was a rough lane.... like very rough. I died 3-4 times, riven got decently fed. Some people like the jg and mid are like "this sucks, but hey whatever". But bot (mostly support Ahri) was delighting in making me their special whipping boy (which yeah, I fed so it was rough for them. But calling people a whore and saying I ruined the entire game for them and I should die..... not necessary).
Finally, I said, "I know I'm bad. I got autofilled so it's rough, sorry." Instant switch. "Oh sorry didn't know. It's fine, we'll be okay. Here's what we need to do - Kayle here's what you can do, here's how you can help, etc."
(The most ironic part was the support ahri saying "Guys cut her some slack," when she was the main flamer)
In the end: You shouldn't have to explain you're autofilled - or have any other explanation for playing poorly - for your team to treat you better. And being nice when you learn that doesn't excuse the toxicity you displayed earlier. It honestly makes your "niceness" really off-puttingly fake.
TL; DR Don't flame, people