KFYS is an Acronym that translates into Keep Fucking Yourself
It is an expression that is used to express your feelings toward a close friend when he claims to have little problems. See the example:
1: Hey What's up ?
2: Ugh, FML fuck my life
1: What is wrong ?
2: Lots of problems, I need to solve them ASAP as soon as possible
1: Well, KFYS then, untill you solve them and if you need help, let me know.