H.M.S. Pinafore, or, The Lass that Loved a Sailor (1878) is one of the most famous Gilbert and Sullivan operettas, poking fun at the British class system. The eponymous ship is awaiting the arrival of Sir Joseph Porter, KCB, who has requested the hand of Captain Corcoran's daughter Josephine in marriage. However, Josephine is in love with the simple sailor Ralph Rackstraw, despite her - and her father's - great horror of feeling affection for someone so far beneath her station. After initially spurning his surprisingly eloquent declarations of love, the two decide to elope and marry on land. However, the sinister sailor Dick Deadeye refuses to believe a captain's daughter should lower herself so, Sir Joseph and the Captain insist on the marriage and the bumboat woman Little Buttercup seems to possess a dark secret relating to Ralph and the Captain...Hilarity Ensues, naturally.
Felony Misdemeanor: Played both straight ("He said 'damme'!"), and for laughs. Dick Deadeye's observations that "It's a queer world" and "Captain's daughters don't marry foremast jacks" are greeted with shock and outrage by the other sailors— even the ones who just said the same thing.
And so do his sisters and his cousins and his aunts ...
Informed Attribute: Josephine knows Sir Joseph is a kind and good man, because he told her so himself.
Inter-Class Romance: A double version of this appears. A middle class woman loves a low class man but at the same time a upper class man is in love with her. Also, a lower class woman is in love with a middle class man.
It Is Pronounced Tro PAY: Ralph's name is pronounced "Rafe" (rhymes with "safe.") This was standard British usage of the time, but has been known to confuse modern audiences, especially in America.
It's Probably Nothing: In HMS Pinafore it was that cat. Specifically, it's that cat-o'-nine-tails wielded by the Captain, who, despite trying to remain concealed, can't disguise his rage when he catches Josephine and Ralph eloping.
Married at Sea: Inverted. Josephine and Ralph intend to elope and get married ashore.
Mind Screw: Assuming Ralph is not the same age as Captain Corcoran, it would be impossible for Little Buttercup to have nursed them at the same time when they were both babies and accidentally switched them around.
Only Sane Man: Dick Deadeye. He's intelligent, highly opinionated, and his purpose is to state what would happen in reality. Of course, since he's ugly, hunch-backed and named Dick Deadeye, he always gets shouted down by his crewmates. He even manages to change the crew's minds by agreeing with them at one point.
Pair the Spares: Subverted, since the Captain establishes early on that he does indeed like Buttercup and outright states that he'd marry her under different circumstances.
However it is then played straight with Sir Joseph and Cousin Hebe.
Precision D Strike: Captain Corcoran in HMS Pinafore, though saying he "never swears a big, big, D" in Act 1, is driven to swear in Act 2 when he learns that his daughter Josephine and crewman Ralph mean to elope. The use of this trope at all is itself a parody, given that the Captain (and in fact all but one of the male characters) are sailors who never swear (well, hardly ever).
"In uttering a reprobation/ To any British tar/ I've tried to speak with moderation,/ But you have gone too far./ I'm very sorry to disparage/ A humble foremast lad,/ But to seek your captain's child in marriage,/ Why, damme, it's too bad! Luckily, there is indeed a consequence for ill-advised asperity.
Rags to Riches: Played straight with Ralph and inverted with the Captain, who were accidentally switched at birth. Both are happy with this development.
The exchange "Never..." "What, never?" "No, never!" "What, never?" "Well, hardly ever..." recurs a fair few times. Counting its two usages in Captain Corcoran's "I Am" Song as one, it shows itself three times.
Take That: The song, "When I was a lad," is a pointed satire on William Henry Smith, the contemporary head of the Admiralty who actually had no naval or military experience, which was of course popularly considered an outrageous appointment for an island nation that depends on its navy.
Sir Joseph: I grew so rich that I was sent/By a Pocket Borough into Parliament./I always voted at my party's call/And I never thought of thinking for myself at all!
Stick close to your desks/And never go to sea/And you all may be rulers of the Queen's Na-vee.
W.H. Smith's reputation never really recovered; even Benjamin Disraeli was reported to have referred to him privately as "Pinafore Smith" on occasion, and during one public engagement the Band of the Royal Marines even welcomed the hapless First Lord with the strains of "When I was a Lad" in defiance of a direct order to do nothing of the sort. Gilbert himself sarcastically denied any connection whatsoever: