FMK Share definition Flag FMK is the acronym for Fuck, Marry, or Kill. Used as a quick gauge to determine the viability of a chick or to categorize a chick. FMK acronymFuck = Avril Lavigne Marry = Jennifer Aniston Kill = Amy Winehouse FMK by SavageNation August 25, 2009 0 0 Get merch Get the FMK mug. Buy Now — $32.95 See more merch