Before Las Vegas became easily accessible, the state of Maryland was a haven for people who wanted to get married with a minimum of restrictions. Many couples in movies went there to get married quickly. In addition to this film, Spencer Tracy and Katharine Hepburn eloped to Maryland in Woman of the Year (1942), and Rock Hudson and Doris Day woke up in a motel in Maryland legally (to their surprise) married in Lover Come Back (1961).
The rhyming slang used by Cary Grant's character is a form of slang in which a word is replaced by a rhyming word, typically the second word of a two-word phrase (so stairs becomes "apples and pears"). The second word is then often dropped entirely ("I'm going up the apples"), meaning that the association of the original word to the rhyming phrase is not obvious to the uninitiated. For example: "Sherman" for an American (Sherman tank = Yank). The exact origin of rhyming slang appears to be unclear, partly because it exists to some extent in many languages. In English, rhyming slang is strongly associated with Cockney speech from the East End of London.
RKO's second biggest hit of 1943, netting $1.603 million, and it was only outperformed at the box office by the vastly lower-budgeted Hitler's Children (1943).
Lux Radio Theater broadcast a 60-minute radio adaptation of the movie on October 18, 1943 with Cary Grant and Laraine Day reprising their film roles.