I am a normal League player. I too have come across some troll teammates and arrogant players. A lot of players usually flame on someone when they do something wrong like building wrong items, playing the champion wrong, doing something idiotic, or anything of the like. When my teammate usually does something wrong, I tell him what he did but I don't get mad and I tell him that it's alright and we'll kick ass later. :)
Sometimes your teammates get mad at you or your teammate says your a "noob" cause you built the wrong item or played the champion wrong.This happens almost every game and you can't avoid it. When playing a new champion or trying a new build, tell them in champion select that you are trying something different. If they're okay with it, go and do it! But if they say no, try to reason with them or just do the new build or champion in a custom game with bots.
In some games your teammates get mad because you or your other teammate feeds the opponent. When a teammate feeds, I tell him that we can still win this and he doesn't need to quit or get mad at himself.
Remember to buy WARDS every game so that you don't get ganked and don't feed. Wards saves lives and reduces deaths. I only knew how to ward or what a ward was (I was level 7 at the time) when I played a game and always got ganked by the enemy Jungler every time I get back to lane. My team got mad at me and told me to ward so I don't get ganked all the time for 30 minutes. I said to my team that wards are a waste of gold but then my teammate explained to me that it could reduce my deaths and I could help more in team fights and get more kills. I learned my lesson and I started warding ever since. Here is a video why you should ward:
