H.M.S. Pinafore

"... to seek your Captain's child in marriage, why Damme, it's too bad!" Illustration from the original 1878 playbill. From left to right foreground, are Josephine, Little Buttercup (with hat), Cousin Hebe (?), Sir Joseph (above, on bridge), Captain Corcoran with boatcloak and cat 'o nine tails, Ralph, Dick Deadeye (with blond beard). The character crouching at right is likely intended to be the Boatswain.

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.

Tropes used in H.M.S. Pinafore include:

All There in the Script: Some character names.
Beta Couple: Captain Corcoran and Little Buttercup, eventually Sir Joseph and Cousin Hebe.
Chewbacca Defense: The entire point of "He Is An Englishman." Not that it helps...
Elopement: Attempted by Ralph and Josephine.
Evil Sounds Deep: Dick Deadeye.
Have a Gay Old Time: See Unfortunate Names, below.
"I Am" Song: "I'm Called Little Buttercup", "My gallant crew... I am the captain of the Pinafore," "I am the monarch of the sea."
- "We sail the ocean blue" is basically a We Are song for the crew.
Incessant Chorus:

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: In The HMS Pinafore, 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.
Married At Sea: Inverted. Josephine and Ralph intend to elope and get married ashore.
Modern Major-General: Sir Joseph, who's had a multitude of successful careers, but has never been at sea before. He's the Ruler of the Queen's Navee.
Oblivious to Love: Sir Joseph to Cousin Hebe.
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
The Pirates Who Don't Do Anything: The Royal Navy.
Precision D Strike: Captain Corcoran in HMS Pinafore, though saying he "never swears a big, big, D" in Act 1, is driven to swear saying "why damme, it's too bad!" 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 Soprano: Josephine
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 as of course popularly considered an outrageous appointment for an island nation that depends on its navy.
Tenor Boy: Ralph
Unfortunate Names: Dick Deadeye. Lampshaded in the script:

"You can't expect a chap with such a name as Dick Deadeye to be a popular character-- now can you?"

Victorian Britain
With Catlike Tread: Carefully on Tiptoe Stealing.
What Do You Mean It's Not Heinous?: 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 foremost jacks" are greeted with shock and outrage by the other sailors-- even the ones who just said the same thing.
Wooden Ships and Iron Men: Parodied without mercy.