Green’s Dictionary of Slang

(orig. US) nonsense!

1917		Hall & Niles One Man’s War (1929) 224: Would I let them send me a cheque! Bunk!
1924		P. Marks Plastic Age 191: Nonsense! Rot! Bunk! Sanford has n’t anything of the sort.
1939		W. Winchell On Broadway 11 Jan. [synd. col.] As for their theories, the Americans have a word for it – ‘bunk!’ . . . . B – as in Baloney, U – as in U-said-it, N – as in Nothin’ doing! and K – as in Horsefeathers!
1949		joke cited in G. Legman Rationale of the Dirty Joke (1972) I 69: ‘Bunk,’ says the little boy. ‘I don’t believe you can do it.’.
1936		‘Josphine Tey’ Shilling for Candles 47: ‘Oh, bunk!’ said Judy.
1972		(con. 1916) G. Swarthout Tin Lizzie Troop (1978) 125: ‘His lungs won’t take much more dust.’ ‘Bunk.’.