Green’s Dictionary of Slang

(US) rubbish! nonsense!

1934		J. O’Hara Appointment in Samarra 163: ‘Fred. Her right name was Fred,’ said Lute. ‘Oh, bushwah on you,’ said Irma.
1938		S. Fisher ‘Not Always’ in Penzler Pulp Fiction (2007) 179: People think big private schools are the ritz [...] Bushwa!
1947		J. O’Hara ‘Not Always’ in New Yorker 11 Jan. 23/2: ‘Oh, I just happened to think that this was Monday and the day after the day after tomorrow is Thursby.’ ‘Oh, bushwah!’.
1953		S. Bellow Augie March (1996) 127: Bushwah, you’re the one she looks at all the time.