There's a good twenty-second pause between the ambassador saying "This is madness!" and Leonidas responding with his famous line. Understandably, people usually omit the long pause when they're quoting the film.
Leonidas full quote is "Spartans! Ready your breakfast and eat hearty, for tonight we dine IN HELL!", but it's commonly shortened to "Spartans! Tonight we dine in hell!" as it is in the trailer.
Dyeing for Your Art: The movie is a gigantic parade of special effects. The monsters, the blood, the surreal colors, none of it is real. But the ludicrously chiseled bodies of the Spartans? Quite authentic. The actors playing the Spartans, as well as the stunt crew, went through Training from Hell in order to earn those abs the hard way. For a sense of solidarity with his actors and to "feel like a Spartan" himself, director Zack Snyder did too.
Genius Bonus: Leonidas calling the Athenians "boy lovers" isn't an insult on their homosexuality. Athens prohibits over-aged prostitutes. Leonidas was saying Athenians are a bunch of wimps for not having sex with "real" men.
Fake Nationality: There is not a single Greek or Iranian actor in a film about a battle between Greeks and Iranians.
Leonidas: (dying) I can see whiskey... a great plate of steamin' haggis... a crappy, overgrown golf course....
This is hardly without precedent, though. In British translations of classical Greek literature, it's traditional to render the Spartan's Doric Greek dialect into English with a heavy Scots accent, to give them the feeling of a more rough, "unrefined" culture compared to the Athenians, who usually speak RP. In American translations the Spartans are usually Texans.
Recursive Adaptation: The film was based on a Frank Miller comic based on his view of the film The 300 Spartans... as in he loved it when he saw it as a child, later saw it as an adult and hated it, so he wrote a comic using his childhood memories as the basis - he used a Nostalgia Filter to enhance the work! The reason it hits the Rated M for Manly button is because it's based around that integral process!