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the act of locking the door behind you when you arrive to your place to lockout someone who may intrude or barge in unexpectedly.
"Hey did you duff the lock? Yeah man, don't worry I duffed it."
by Pants007 January 20, 2009
Dark brown or black cannabis remaining in a vaporizer bowl after vaporizing. The duff, which still contains some THC, is recycled rather than discarded by stingier enthusiasts.
Whoa, don't toss that duff, man! I'm saving that to make hash.
by John Woods August 25, 2008
(Da Ugly Fucking Friend) A term to describe the less attractive females another female will have in company to make her seem more attractive or just a less attractive friend to more attractive female. (Originating in Bear, Delaware)
Jon: "Hey! did you see that girl that just walked by?"

Brandon: "Which one?"

Jon: "The one in the middle bro!"

Brandon: "Oh yeah, but she's only a 6 on a scale of 1-10 without those DUFFs."

Jon: "Yeah her other friends were pretty ugly."
by Boogey Man Brown October 05, 2011
to throw a severe beating to another person or group. Used with mal intent or to beat the ass's of.
"If you don't shut the fuck up, i'm gunna duff your dumb ass"
by DamionFK December 01, 2006
D.U.F.F stands for designated ugly fat friend
Kassie wants to feel good about herself so she has a D.U.F.F
by Nick November 22, 2004
Dumb Ugly Fat Friend: Usually accompied by the attractive girl that you actually want to talk to.
That girl is so hot, but she has that Duff standing next to her.
by Cody August 23, 2004
Designated Ugly Fat Friend
Timmy: Chelsey and sarah are so hot. why does she hang around with heather. she is so fat.
Bryan: Heather is their DUFF to make them look better
by shortman94 March 29, 2010