UK, 1921—‘frogspawn’: a jocular appellation for ‘tapioca pudding’ (also for ‘sago pudding’)—originated in schoolchildren’s slang—refers to the fact that both tapioca pudding and sago pudding very much resemble frogspawn, i.e., a soft substance like jelly which contains the eggs of a frog
USA, 1986—ugly spectacles, in particular army-issue spectacles—the image is that those spectacles are so ugly that nobody would want to make a baby with somebody wearing a pair—also ‘BCGs’
USA, 1966—a (13th-birthday) party held for a dog—a blend of ‘bark’ (the sharp explosive cry of a dog), and of ‘bar mitzvah’ (the coming-of-age ceremony for a 13-year-old Jewish boy), or ‘bat mitzvah’ (the equivalent ceremony for a Jewish girl)
USA, 1975—to hastily or furtively leave a restaurant, cafe, etc., in order to avoid paying for one’s bill—also used as a noun, especially as a modifier—has also been used of meals eaten quickly
Lancashire, England, 1939—used in similative and comparative phrases such as ‘as —— as soft Mick’ and ‘more —— than soft Mick’, the noun ‘soft Mick’ (also ‘Soft Mick’) indicates a great quantity or degree
Australia, 1944—the customary bout of hasty drinking in public houses at the end of the working day, occasioned by the former six-o’clock-closing regulations
Australia, 1937—very scarce—‘rocking horse’: a toy horse mounted on rockers or springs for a child to sit on and rock to and fro—this phrase has come to be also used in British English and American English
USA, late 19th century—these phrases a) express mild remonstrance towards a person who has left a door open, exposing others to a draft; b) indicate that a person is behaving in a rude or uncouth manner
USA, 1992 (1981?)—adjective: primarily but not strictly vegetarian—noun: a person who follows a primarily but not strictly vegetarian diet—a blend of ‘flexible’ and ‘vegetarian’