An abbreviation of Friday Night Funkin', basically a newgrounds.com where you "rap" against a kid with a gun, an attractive dad and milf and two spoopy kids
"Hey man wanna play some fnf"
"Nah sry it's too hard for me"
More commonly Known as Friday night Funkin, only degenerates, lonely, societal rejects play this game, where a hornyteenager trys to avoid blue balls, whilst failing to get a girlfriend, because no one who plays the game has one.
Person 1: FNF is sooooooooo cool!
Person 2: Are you sure
Person 1: Yeah, Why?
Person 2: Check Urban Dictionary
Person 1: *dies*