UK, 1882—‘penny’ refers to inexpensiveness, and ‘puzzle’ to the mysterious nature of the ingredients—perhaps also in humorous allusion to ‘penny puzzle’ in the sense of a puzzle-card sold on the street for one penny
UK, 1839—jocular variant of ‘penny-a-liner’ (i.e., a journalist who was paid at the rate of a penny a line, a person who produced mediocre journalistic work) with the implication that such journalists fabricated falsehoods
1546—of little or no worth—here, ‘pudding’ refers to a sausage-like mass of seasoned minced meat, oatmeal, etc., stuffed into a prepared skin and boiled
USA, 1937—informative material presented in an entertaining way at working-meetings (and later at other types of gatherings) organised by Shell Oil Company—a blend of ‘information’ and ‘entertainment’
late 18th century, in the context of piracy: to walk along a plank placed over the side of a ship until one falls into the sea—hence, figuratively, early 19th century: to be forced to resign from one’s office or position
nonsense, rubbish—USA, first decade of the 20th century—probably a euphemism for the noun ‘bullshit’, with the noun ‘dust’ used in the sense of ‘rubbish’, ‘garbage’
1910: a cheap and common watch—hence (from 1922 onwards) used in various phrases referring to silliness, reliability/unreliability, erraticism, cheapness, funniness
refers to a person who is ignorant or dismissive of the hardships of others—alludes to the phrase “let them eat cake”, attributed to Marie Antoinette, wife of King of France Louis XVI