1. To get a stamp on your completed homework.
2. To act crazy and/or insane while teaching or just talking in general.
3. To yell at one's smart board.
4. To flick off one's class.

5. To stand on a desk to feel if the air is working.
6. To teach "shit"
7. To throw markers at ghetto kids.
Person A: "Yes I derfed my homework!"
Person B: "Ugh, lucky, I skipped one problem."

Teacher: "You guys forgot your calculators?!!!!" "YOU'RE ALL LOSERS!!!!!!"

Teacher: (to smart board) "WHY ISN'T THIS THING WORKING?!"

Students: (to teacher): "Happy Birthday!"
Teacher: *flicks off class and walks out*
by calculusstudent November 23, 2012
Kick-ass cartoonist. Draws & writes 'The City'. Created 'My Friend Dahmer'. Not respected by enough people.
"Derf rocks."
by Raewyn June 14, 2004
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!
by Jay Young March 07, 2008
The process of: executing a handstand; masturbating during handstand; ejaculating in direction of mouth; regaining post orgasm senses and gracefully avoiding free-falling wad. A professional sport in parts of Oregon.
Did you hear Sunshine Bear died while in the derf last night?

No…how?

His dad caught him in the act and beat him to death.
by Lupus Lavign. July 12, 2006
A wonderful humourous individual. Usually an adult. The kind who would make an excellent coach, parent etc.
We should be so lucky as to have him as a coach, he's a derf.
by rellim April 07, 2005
A bold and corageous urban warrior. A fierce enemy.
We should all strive to be a Derf.
by Pedroumbrella October 18, 2007
a fag. one who is constantly a jerk and says bad things about others. sweats profusely, especially from the palms. can be made nice by offering an ultimatum.
I hate that DERF! He always talks about "that guy" that he isn't supposed to talk about.

I hate that DERF! He is so mean!

I hate that DERF! He is writing an incredibly rude and secretive novella about me.

I hate that DERF! Today, he was so annoying I had to pencil-slap him...like 25 times.
by Novella Character #1 May 20, 2008
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

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