POSITIVE, adj. Mistaken at the top of one’s voice.

Ambrose Bierce (1842-1914?) American writer and journalist

“Positive,” The Devil’s Dictionary (1911)
    (Source)

Originally published in the "Cynic's Word Book" column in the New York American (1906-03-16) and the "Cynic's Dictionary" column in the San Francisco Examiner (1906-03-21).