What is the worst thing you can say to someone without being toxic

You should just try to help that player... No need to even go the toxic route at all.

i.e. "Hey, maybe you should ward one side of your lane because J4 is ganking you from that way. Once you place the ward sit on that side so your safer. If you see him coming, back up till he leaves. We will come help you so hang in there man!"

Thats what I do, and i'd say about 70% of the time it works. Yeah you'll get the occasional, "STFU BITCH MUTED" but at that point there really isnt much you CAN do for that person. Just mute them and move on with the game.

Hope this helps!

Saying that someone sucks is being toxic as it is not a form of constructive criticism. It is just verbal bashing.