Stands for keep yourself safe.
Person 1: I'm going out tonight
Person 2: Be sure to kys
"kys" is an abreviation for keep yourself secure, its usually used when theres a possibility of someone getting injured by causes such as hurricanes and other natural disasters.
Hey Luke, have you seen that theres a flood warning near where you live, kys man.
It’s basically a death threat to reset character,if you know what I mean,sometimes it means keep your self safe
YOU SHOULD KYS NOW!!!!!+kys!