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1.
A sound caused by a large force acting upon something else. It is a manly sound and can be used verbally to describe large, heavy or masculine objects/foodstuffs/people.

Can also be used to describe excessive speed, height, turd size, uglyness, etc.....
e.g.1

Mate, look at the size of that chip butty! BFFFT!

e.g. 2

Your car is well fast, like BFFFT!

e.g. 3

Whooaa!! She got one massive ass. BFFFT!

e.g. 4

BFFFT!!!!!
by Jeff 'No Dice' Painmaker April 15, 2010