MONDAY, n. In Christian countries, the day after the baseball game.
Ambrose Bierce (1842-1914?) American writer and journalist
“Monday,” The Devil’s Dictionary (1911)
(Source)
Originally published in the "Cynic's Dictionary" column in the San Francisco Examiner (1904-09-03) and the "Cynic's Word Book" column in the New York American (1904-09-09).