derf 

noun: An inept or foolish person, someone who doesn't use their head. On the PLATO computer system of the 1970s (which in many ways foreshadowed the Internet), a derf was one who left their computer terminal without logging out.

verb: On PLATO, a prank played on a derf. Sending out unpleasant or embarrassing messages under the handle (or "signon") of a person who'd forgotten to log out. Or ruining programs they've been working on.

noun: Wow, "Melvin of MIT" is a real derf! Look, he just walked out and left his terminal logged in.

verb: Hey Melvin, I just tried to run one of your programs and it looks like somebody got into it and put in a bunch of porn. Looks like you got derfed!

derf by Jay Young March 8, 2008

Derf 

another way to say the word "duh" almost like obviously

Person 1: Wait why are we going to the mall?
Person 2: To go shopping, derf!!!

Derf by yeah3xyeah3xyeah3x March 28, 2011

Derf 

One stupid ass fucked up bitch, who doesnt know what she wants, lies all the time, tells you she likes you... but then sometimes wants to get on other people...

Man... she is such a Derf!

Derf by Derf Hater July 12, 2006

derf 

a retartedly, annoying white girl; usually very ugly

that stalker gurl is a mad derf

derf by Anonymous July 12, 2006

derf 

The reverse of the name "Fred". Commonly used by people who are either trying to be silly, those who think that it's a cool name and didn't like being labeled a "Fred", and those who truly think that it's a great pseudonym and no one will ever figure it out.

Overheard at a trekkie convention:

Fred: "Dude, I'm so awesome, I'm gonna reverse my name and call myself Derf."
Clueless friend: "Dude, that's awesome!!!"

derf by Octoboi July 30, 2007

Derf 

A derf is another word for the unwanted. the person no one wants/need. the loner. the suspected pshyco killer. it can also be another word for tool, widely known as somebody no one needs (annoying). an extremely BIG insult.

Can you believe that effing Derf? what a tool!

Derf by CoUnTrYwOrLd July 7, 2011

derf 

(Definition 1): The extra skin that allows your balls to swing out, so you don't shit on them. (Although usually covered in hair, there have been reports of hairless and albino derf spottings in the wild);
(Definition 2): sweaty, stinky, beneath you, Flappy Fringered Bassist

(Definition 1): This Guy I know was in a bad car accident and broke his derf. Doctor told him it might never be the same.
(Definition 2): That guy they caught spanking it in the Mens room is such a Derf.

derf by Jaysmoka April 29, 2007