The term is also interchangable with similar terms such as: durp durp, hurp-a-durp durp, and da durp durp.
Person 1: "Dan thought that Iraq meant a woman's chest."
Person 2: "Hurp a durp."
Person 1: "Who's Madonna?"
Person 2: "Hurp a durp!"
Also an exclamation at one's own stupidity or the stupidity of a close party. Normally "hurpa-durpa-durp" (with added '-adurp's for added emphasis). Must be said in the fashion of a mongoloid.
Not to be confused with "hinga-dinga-durgen".
B: "Stop being such a hurpadurp."
A: "OMG! Them things are liek only £20!"
B: "No, it says they're £200!"
A: "O right, I see... hurpa-durpa-durpa-durpa!!! *X-z*"
Example2: Michael: Bro, ima herp a derp ur face dick!
Nick: bring it foooo!