I will remind you that there is a tribunal system (inb4 loltribunaldoesntwork) that is designed for players to identify toxic players and report them for their unsportsmanlike behavior. You are encouraged to do this as much as possible whenever you have a negative player experience.
I will also remind you that there is a mute button. Yes, I know. It's frustrating to have to use a mute button and break down communication on your team. But it's been proven that your performance only continues to grow worse as you are harassed. If a player can't offer you any constructive criticism, then you have no business talking to them and they should be muted.
That being said, sometimes people really aren't being grumps or jerks. Sometimes, players will offer you constructive, realistic criticism in the game. For instance:
"Don't go out alone."
"Ward the river."
"Ward your lane."
"Stop chasing kills"
"Group and fight as a team"
"Focus on farm."
"Stay at tower."
If players head you this advice, and you refuse to take it and you still end up falling behind and doing poorly, they will get frustrated. And rightly so. Now, don't mistake me. This does not give a player a license to begin verbally harassing or abusing you. League of Legends is a highly competitive game and some people use normal blind and draft to practice their teamwork coordination for use in ranked. People would rather not try things out in ranked because it could result in lost ranking if it doesn't work out well. This is why some people appear to take normals more seriously than others.
My final thought: Ragers and flamers are everywhere. Your best weapons against them are to mute and report. Usually, however, what I find is that a lot of players who engage in this kind of negative behavior are actually insecure about their own performance in the game or their ability to work as a team. A lot of players feel that if they do not start flaming the feeder or calling out peoples' mistakes, then they will get looked at as the feeder or "noob." It's a psychological mentality of "They won't possibly think I'm bad because I'm calling everyone else bad!" This is flawed, juvenile logic at best but it exists in this community. Riot has stated time and time again they want to leave it to the community to gauge for themselves what behavior is acceptable and what is not. That's why it's up to us as a community to stress the tools available to you against these types of negative players and demonstrate that a toxic, unsportsmanlike environment will not be tolerated on the fields of justice.