YFKI 

You Fuckin' Knows It als Goldie Lookin' Chains (GLC)

"Dude, I JFYM and 404's Sister!"
"Oh snap! YFKI"

YFKI by Intertron December 11, 2004

YFKI 

You fuckin know it

Friend 1: "you wanna go to vegas next weekend?"

Friend 2: "YFKI!"

YFKI by Sahbatoge May 3, 2013