OK. I have two opinions on this. Often bitches who are playing a mediocre-bad game will flame the most to remove attention from them for playing badly. If there is a team with a Fizz 1/7/2 for instance and a Zed 3/4/2, the Zed will shout at the Fizz every time he dies, will blame the Fizz whenever he dies, tell the Fizz to never play again etc.
If you have a team that is not all bad, but is only getting killed by one person on the enemy team, thus feeding them, you will start to get an immediate in balance in the teams. Then Fizz comes along with a score of 1/2/2 and gets killed twice easily in the mid lane. Now the entire team except for the bot ADC's who always seem to be nice will flame. The Fizz gets stressed out, tries to get kills desperately and then just feeds even more. Now the team are asking everyone to report him and then you get one asshole who completely disregards that the feeder is in the same ELO as him and is obviously not way worse than him. This happens a lot in ranked bronze games. People think because they play SOLO queue and because they are now ranked they can just be arrogant narcissists and flame. But I find this completely stupid as if you got to level 30 (Which you cannot do if you are shit) you are not that bad. So these flamers are just angering the feeder and making them play even worse.
Then you get assholes who surrender all the time. GUYS! SURRENDERING IS NOT THE OPTION! Just loose the fcking proper way by getting your Nexus destroyed. Surrendering just makes you look like a %%%%%!!!!!! These people then spend all their time waiting for when next they can start a vote rather than actually playing. They then spam the chat asking the team to surrender when they do finally vote. So please don't do this.
Then you get the worst of the worst. I call these people FckFacedCunntLickingAssholeMFckers. These people go AFK when the game has a feeder in it. They actually normally stay online but just sit in the base. These people don't help the game and get reported more than the feeder.