"I will murder your whole family."
"I'm gonna kill you." "I'll gut you." "You're a cockroach." "What was that? Run straight into the tower?" "Oh, before I forget, what, uh... rank are you, exactly?"
These are all completely acceptable things to say in chat, and there is no argument you could present to the contrary. They're just champion quotes.
Edit: You'd have to be awfully socially inept, I'd even say a downright idiot, to think saying these to people in League while playing the game is anything at all like saying them to people who don't play League in person.
