Poppycock
Etymology
American English of the mid-1800s, borrowed from a Dutch dialect word "pappekak," from "pap" ("soft") and "kak" ("dung"). So the literal image is soft dung — a polite-sounding word that is quietly crude at the root. Speakers who reach for it as a genteel alternative to stronger language rarely know they are saying something earthier.
noun · /POP-ee-kok/
Nonsense; empty or foolish talk.
What it names
Confidently stated rubbish — mild enough to say anywhere, with a hidden bite once you know its roots.
Example
He called the whole forecast poppycock, then quietly moved his money out of the market.
Related idea
Balderdash and poppycock are near-synonyms; poppycock is the one with the sneakily scatological origin.