OXFORD DICTIONARY
, adj. Brit. sl.
1 worthless, counterfeit.
2 useless, broken.
, v.tr. sl.
1 Brit. Golf mishit (a shot, a ball); bungle.
2 Austral. steal and alter brands on (cattle).
duff up sl. beat; thrash.
perh. back-form. f. DUFFER
THESAURUS
arse, bad, beat, behind, bilk, bottom, broken, butt, can, cheat, counterfeit, cozen, defraud, diddle, do, dud, fake, false, fanny, gyp, inoperable, inoperative, overreach, prat, rear, screw, tail, unworkable, useless, worthless