The Bronx?
No, thonx!

Nash’s couplet is a compact example of his comic method: a familiar proper noun (“The Bronx”) is treated as if it were an ordinary English word that ought to rhyme, and the invented reply (“thonx”) delivers the joke by forcing a rhyme where none naturally exists. The humor depends on playful mishearing and on the absurdity of answering a place-name as though it were a conversational prompt (“The Bronx?” / “No, thanks!”). It also gently satirizes the way New York borough names can sound brusque or opaque to outsiders, turning local geography into a linguistic gag.