An acronym meaning Flipping Across the floor. Used to express extreme laughter while chatting. Only to be used in situations that are actually too funny for a basic lol or rofl.

Other Uses:
Fatf-copter
Fatf-jet
Person #1 Today i fell down in front of the entire school and my pants ripped, i was so embarrassed. =

Person #2 Fatf !!
by -KILLALL- December 3, 2009
Get the FATF mug.