From http://www.answers.com/poppycock&r=67 :
pop•py•cock (pŏp'ē-kŏk') n. Senseless talk; nonsense.
[Dutch dialectal pappekak : pap, pap (from Middle Dutch pappe, perhaps from Latin pappa, food) + kak, dung (from kakken, to defecate, from Middle Dutch kacken, from Latin cacâre).]