In modern internet vernacular, a generic all-purpose phrase that roughly equates to "duh," and can be used in a variety of situations to indicate stupidity.
Person #1: That horrible website somethingawful.com stole my intellectual property by taking pictures that I had on MY WEBSITE and manipulating them in offensive ways with Photoshop! I shall send them a legal threat posthaste!
Person #2: (summarizing Person #1's statement for others) HURF-DURF INTERNET LAWSUIT
Exclamation. "DURRRR YOU'RE AN IDIOT."
Origin: Metafilter, 2005. "Hurf Durf Butter Eater" was the self description of the notorious Metafilter user U.N. Owen when she was complaining about how people called her fat when it wasn't her fault she was allergic to exercise. Used as an noun earlier (see other entries).
Arnold: I'm not leaving this place until I get my refund!
A person that is not to be taken seriously.
Jerkden: Play my card game!
Kiko: Well, I don't know how...it's complicated, and I don't feel like learning that shite.
Jerkden: It's okay, be like Dackson. He's no good at the game, but he plays anyway and has fun.
Kiko: Well, Dackson will be the lone hurf-durf; I'm not playing!
Jerkden: Suit yourself.
*Kiko punches Jerkden*
Hurf (v) From Old English: To quietly expectorate
Durf (n) From Old Norse: The mixture of alcoholic beverages in the stomach after a night in a lowly tavern
Hurf durf: a sound often heard eminating from public toilet cubicles at 3:30am on a Saturday morning
(Dad) How was your evening, son?
(Son) Well I hurf-durfed at the Slug'n'Lettuce, and after that Marie wouldn't shag me.