TFW I learned what Karthus's Ban quote is:

"Ahh, the Kiss of Death"

Found this out because enemy ACTUALLY BANNED Karthus on me XD

Though to be fair I think it was a riven top who did it and Karthus top will DUMPSTER a Riven :P

On a side note, it seems weird for a ban quote isn't it? I'd kinda prefer his joke line: "I'm putting your name into my little black Necronomicon"