Present participle of crap; defecating or, in slang usage, talking nonsense or failing at something.
From Middle English crappe meaning 'chaff' or 'residue,' from Old French crappe. The scatological meaning developed in the 19th century, while the 'nonsense' meaning emerged in 20th century American slang.
Despite popular belief, this word has no connection to Thomas Crapper, the Victorian plumber - that's just a coincidental surname. The word's evolution from 'chaff' to its current meanings shows how language often takes the most direct metaphorical path from agricultural waste to other unwanted things.
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