Poppycock is American slang for rubbish or nonsense, and dates from 1863, according to the OED. Its etymology derives from Dutch that was spoken in the northeast of America when Dutch settlers were there. The 'poppy' part derives from either poppe meaning doll or girl, or from pappe meaning soft. The cock part derives from kak meaning excrement. Thus, literally, it's either 'girl shit' or 'soft shit'. The former is sexist and offensive, so the 'soft shit' etymology is the more favoured. Dutch settlers brought the word to America in the 1600s, and Americans anglicised and exported it to Britain as poppycock in the mid-19th century. Mercifully, poppycock is now devoid of all scatological connotations, except, of course, for those who wish to delve into its etymology.