What does the term ?hoist the black flag? by H. L. Mencken mean?
The quote, from H. L. Mencken?s 1919 Prejudices (First Series), is in full: ?Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats.?
To start with hoisting a black flag really buries the lede! To ?hoist the black flag? is a reference to piracy. The Jolly Roger?s history is well covered on Wikipedia here, and also shows the many documented designs used, including the use of plain black flags by pirates. Why pirate?s flags came to be called ?The Jolly Roger? is likely because of its first documented use in Capt. Charles Johnson?s A General History of the Robberies and Murders of the most notorious Pyrates. A black flag was a powerful symbol and object at that time.
Image by Oren neu dag [CC BY-SA 3.0]
Ships use flags even today as a method of communicating visually with one another at sea. By international law, ships must fly their national flag to aid in identification. Pirates belonged no nation, renouncing any authority but their own. A privateer has been commissioned by their government to go forth and wreak havoc (and not the same). A pirate?s flag was not only identification but was also a symbol of terror because it meant ?no quarter given,? essentially, it meant to communicate that the pirates intended to catch the other ship, board it and kill everyone on board.
H. L. Mencken was a very funny writer, critic, essayist, and observer. His book, Prejudices (First Series) can be read in full here via The Internet Archive or downloaded in one of several formats from the same source. The phrase ?hoist the black flag? did not originate with him, but he did apply it in a humorous and poignant way.
 Jolly Roger
 Prejudices: first series: Mencken, H. L. (Henry Louis), 1880?1956: Free Download & Streaming: Internet Archive