There is absolutely no need to "defend yourself" in an anonymous environment.
I'm not trying to come off as rude or harsh, but when a toxic player is egging you on and belittling you, your first action should not be "I'm going to reply to this player". You wanna know why? Because that's EXACTLY what they want you to do, it's a game to them and you fell right into their trap.
A given example is if your Kha'zix jungle is taking Skuttle crab level 2, where the enemy jungler is there to contest and Kha'Zix dies, and his response to the situation is to blame you, don't even bother responding. Don't defend yourself, because the truth of it all is, he won't even remember your damn summoner name after a minute of pressing "play again". He won't even remember what you even played as an hour from then, nor remember the game in general a day from now.
Believe me, I have sympathy for you guys who easily get offended because you just want everyone to like you, or whatever the case may be, but there is literally no excuse for you to retaliate. The muting option is there for a reason, and to be frank with you, 9 times out of 10, the chat option only causes problems, so unless you're playing normals to make friends or in a party with someone, just do yourself a favor and mute everyone in the game.
Putting your account on the line because someone was an ass in game isn't worth it. Those are the type of players who are just so upset with themselves to the point where they vent their frustration on a video game, so it's not worth your time and effort to reply. I do pity them, I really do, but it's just how the internet is, and you trying to defend yourself is only making the situation worse for you, because I can assure you, they are going to get punished regardless depending on what they type.
Again, my purpose of this post was not to hurt those who are truly just trying to defend themselves. The purpose of my post was to protect your account, because in actuality, the mute button is the best way to defend yourself. If someone was screaming in your face in person, wouldn't you just wish you could turn their volume down or put a piece of tape over their mouth?
The person who gets mad first loses, always remember that.