In my experience as a new player i have ran into so many toxic people it has been surprising. I have ran into maybe 2 people that were understanding of my n00bie status. It's very sad.
I have been playing maybe a month and a half, reached level 30 and when i started playing ranked games it has just been overran with rude, obnoxious people. It's like every game so far in ranked has been a horrible experience. I even let my team know before hand that i am new to the game haven't been playing very long and if i make mistakes I'm sorry before the match even starts. I'm sure even the best players have bad games or they get matched up with someone that is better then them on occasion.
The only advice i have for someone wanting to be rude or berating a player for their mistakes is, you should just be quiet about it unless your willing to offer constructive advice on what they are doing wrong and how they can fix it in a nice manner. I can almost guarantee once you start harassing the player that made a mistake and you continue through the entire match you will get a loss. i know when someone starts berating me and telling me how bad i am i play even worse, not on purpose just i get frustrated and my play suffers. I have seen it happen to others also and I'd be willing to bet anything i had that these players berating others have had bad games and I'm 100% positive they made stupid mistakes when they were new also.
So far the community i have met there have been very few good teammates and seems to be overrun with rude, obnoxious people who i would love to meet in real life and have them talk to me like they do in the game. I have a feeling they wouldn't be so free with the way they talked to me.