verb: to do something stupid, immature. to lack rational judgment.

noun: the space underneath a man's scrotum before his anus; a normal person minus reason and accountability.
I can't believe I stapled my scrotum to my chair again. I really pulled a derf.

Dude, you only worked 3 hours today, don't pull a derf.
by Derfilicious December 16, 2007
Synonym for taint. The space between the balls and the asshole
"She licked my derf"
by Greg T January 29, 2005
1: A ridiculously stupid or dumb person who doesnt understand anything, such as a ditz. 2: Someone who should be a stereotypical blonde, minus the blonde hair.
Person 1: Did you hear that Amie said that 2 + 2 = 3?!
Person 2: Yeah, she's such a derf
by BSandB4LIFE January 01, 2004
a exclamtion of stupidity...see also duh
"oh i remember where i put that....derf!"
by jaci inspired by alex February 24, 2003
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!!!"
by Octoboi June 26, 2007
(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.
by Jaysmoka April 15, 2007
"Derf" is a term that refers to the hair that grows on the perineum (aka "chode" or "taint")
Make sure you shave your derf before asking a lover for a rim job.
by blanatan July 16, 2006
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