What is Yfl?
1.
You Fail Life
Since you really don't want to waste any more of your time on people who fail at life than necessary, YFL is there to shorten this burden.
Idiot: "GOD DAMN, I JUST LOST A BET ON THE DETROIT LIONS"
Suave, young gentleman: "YFL."
See
2.
You Fucking Liar
Commonly used when talking in IM or even in a regular conversation.
Bob: I think your clothes are nice.
Mary: YFL Bob. I know what you're really thinking.
See