‘double Dutch’, 19th century—from ‘Dutch’ in the sense of a language that few people can speak, and ‘double’ as a mere intensifier—‘High Dutch’, 17th century—loan translation from French ‘haut allemand’ (= ‘High German’), used in the sense of gibberish
USA—‘to go Dutch’ (1907): to have every participant pay their own expenses, or share expenses equally—via ‘to go Dutch treat’ (1887), from ‘Dutch treat’ (1873): a meal, etc., at which each participant pays their share of the expenses—from a German practice
UK, 1797—strength or confidence gained from drinking alcohol—alludes to the drinking habits ascribed to the Dutch—one of the phrases in which ‘Dutch’ is used derogatorily, largely because of the enmity between the English and the Dutch in the 17th and 18th centuries
UK, 1967—chiefly British—‘bums on seats’: the members of an audience, at a theatre, cinema or other place of entertainment, especially when viewed as a source of income
1916—from ‘brownie’, i.e. a benevolent elf that supposedly haunts houses and does housework secretly—not from the fact that the uniform of the junior Girl Scouts and Girl Guides is brown
first recorded in the Los Angeles Times (California) of 15 March 1951—possibly from ‘brownie’ in the sense of ‘a benevolent elf that supposedly haunts houses and does housework secretly’
USA, 1950s—The noun ‘doggy (or doggie) bag (or pack)’ denotes a bag, provided on request by the management of a restaurant, in which a diner may take home any leftovers; apparently, these leftovers were originally intended for the diner’s pet dog.
late 16th century—from early modern Dutch ‘maelstrom’ (now ‘maalstroom’)—originally a proper name designating a powerful whirlpool in the Arctic Ocean, off the west coast of Norway, which was formerly supposed to suck in and destroy all vessels within a wide radius
USA, 1946—‘to have, or to get, egg on one’s face’: to be, or to get, embarrassed or humiliated by the turn of events—refers either to having eggs thrown at one’s face or to yolk stains left on the face after the careless eating of a soft-boiled egg
U.S., second half 19th century—from the story (1850) of a man who, having declared that he could eat anything, was challenged to eat crow; the crow he had to eat was seasoned with snuff, so that the man gave up after one bite, saying “I can eat crow, but I’ll be darned if I hanker after it.”