The most common toxic commentary in LoL starts with the rhetorical "Why?"
"Why?" An innocent question when asking someone for advice, but in League players tend to use it in the rhetorical sense in order to publicly shame another player.
It comes in many forms: "?" "Why?" "WHY?" "OMG WHY?" "Why did you. . ." flash/ult/back/go in "Why didn't you. . ." go in/back/buy that certain item Spamming of the "missing in action" ping over someones' character.
If you want to help lessen toxic behavior avoid the rhetorical "why?" questions in all its' variations. It's just a passive aggressive form of verbal abuse.