cup of joe

Uncertain. * Possibly a shortening of "cup of jamoke", from java + mocha: this origin was given in a military officer's manual from 1931, around when the term first appeared. * Alternatively, perhaps a use of joe (“fellow, guy”), signifying that coffee was the drink of the common man. * Another theory suggests that US soldiers in World War I (1914-1918) referred to a serving of instant coffee made by the G. Washington Coffee Refining Company (founded in 1910) as a "cup of George", and that the common abbreviation of the name "George" ("Geo.") was then read as "Joe". * Another theory derives the term from Josephus Daniels (1862-1948), the Secretary of the U.S. Navy who abolished the officers' wine mess and thus made coffee the strongest drink available on ships. Snopes considers this unlikely because it says there is no attestation of the phrase "cup of joe" until 1930, 16 years after the 1914 order banning the wine mess. Confusingly, some other sources consider the Daniels derivation unlikely for the opposite reason: they say "cup of joe" predates the order.

来源：wiktionary