- to give a deliberately deceptive appearance to; misrepresent; fake.
- British. (in golf) to misplay (a golf ball), especially to misjudge one's swing so that the club strikes the ground behind the ball before hitting it.
- to steal (cattle).
- (formerly) to alter the brand on (stolen cattle).
- to cheat someone.
Origin of duff3
1830–40; back formation from duffer, in the slang senses “something inferior or counterfeit” or “a peddler of inferior goods”
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for duffed
Its position rather affected my follow-through, so that I duffed my stroke and lost the hole.The Complete Golfer 
- a thick flour pudding, often flavoured with currants, citron, etc, and boiled in a cloth bagplum duff
- up the duff slang pregnant
C19: Northern English variant of dough
- slang to change the appearance of or give a false appearance to (old or stolen goods); fake
- Australian slang to steal (cattle), altering the brand
- Also: sclaff golf informal to bungle (a shot) by hitting the ground behind the ball
- British informal bad or useless, as by not working out or operating correctly; duda duff idea; a duff engine
See also duff up
C19: probably back formation from duffer
- slang the rump or buttocks
C20: special use of duff 1
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for duffed
"buttocks, rump," 1830s, of unknown origin.
Online Etymology Dictionary, © 2010 Douglas Harper