An expression usually meaning "Duh" or "Dur" Or to be Politically Correct "Of course, you effing idiot!" usually followed by a smack. Sometimes used as a filler word, usually giving or taking a "be" as a pre-fix or "adurp" as an add-on.
Idiot: "hey dude, I think he's dead..."
Normal Guy: "Durp, you fuckin' retard! Now Help Me With The Body, before my parents get home."