A shortened version of "Keep Yourself Safe"
Richard: bro, kys next time ur going out i heard about a murderer in our part of town
Tom: did you just tell me to kill myself
Richard: thats optional
kys means kill yourself
take this an as example.
you are trash talking your friend and he says shut up you can say:
bro go kys (kill yourself) it will gravely hurt his feelings
man 1: kys
man 2: what?!
man 1: keep yourself safe
man 2: oh kys too