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).