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1.
abv. for Designated Ugly Fat Friend; Term men use to describe a fatter, less attractive friend, a woman brings with her to a party or social gathering to make herself look better by comparison. In some cases the more attractive woman will not "put out" for any male, unless one of his friends "takes one for the team" and "hits" the Duff.
C'mon take one for the team and hit that Duff (D.U.F.F.), I'll buy you lunch tomorrow!
by Dr. Slappy McGee III Esq. March 06, 2006
 
2.
The drums signifying the cliffhanger at the end of Eastenders.
The end of Eastenders.... duff duff....
by rkelly23 January 27, 2010
 
3.
A Scandinavian drinking game that can be played by two or more players.

Played in a circle the participants hit a beer can against their head twice with considerable impact (hence duff duff) and then pass the same beer can to their left. The next participant does the same and that continues until the can springs a leak.

The person whose head caused the leak then needs to open the can and down it.

The player to the loser's left takes a fresh can and the game continues.
This drinking game should only be played by skilled experts.

Duff Duff is often played at men only events such as but not limited to: camping trips, bucks parties and festivals.
by Gazcap January 24, 2012