I am going to ask you what is toxic.
Is it toxic to say GG at 20 min cause you did poorly and you think the game is over? (that being negitive)
Is it toxic to call some one out on constantly questionable play? (could be considered blaming)
Is it toxic to have to afk due to an emergency.(well afk)
We all(thinking people) agree that racism, sexual conduct, pure rage outs(flipping tables) is toxic. But you said being negative is toxic. I think that being negative can be practical. We all have had games where someone said we are throwing guys bad paly after bad play when ahead. Technically they are be negative therefore under your post toxic.
Lets pull back a bit from this buzz word a bit. I know that the word toxic is in vogue since riot actually uses it. Before league we do not use the term toxic. We used more precise terms rager, afker, know it all, asshole, buzz killer/kill joy ect. To be toxic means i can be any one of thing or more that I just listed. i think the term Toxic has grown out of its original meaning. Lyte and his team first used it to explain the worse of the worse. Now it includes the guy having a bad day.