look up any word, like doxx:
 
1.
A term used on tumblr and other sites usually posted in conjunction with a picture of attractive people/persons maintainer of said site would have no qualms fucking
Person 1: I'm going to post a picture of some cute hipster chick on tumblr! what should I tag it as?

Person 2: why not use unfff?
by whatnotery August 19, 2011
 
2.
Scientifically proven sound a man makes when kicked in the testes.
Captain Falcon: FALCON... PUUUUNCH AT BALLS

Innocent bystander: OH SHI--UNFFF.

-Graphic Image-
by The Captain Falcon in example. September 27, 2010