"You canker blossom!" 3 Shakespearean Insults
"to dismiss lightly and contemptuously," 1827, a slang reduplication of dismissive expression pooh. Among the many 19th century theories of the origin of language was the Pooh-pooh theory (1860), which held that language grew from natural expressions of surprise, joy, pain, or grief.
To dismiss lightly and contemptuously; airily deprecate; deride: I don't poopoo his talent, just his character (1827+)