Green’s Dictionary of Slang

(orig. Aus.) an excl. of extreme surprise, annoyance.

c.1943		S.J. Baker Aus. Vulgarisms [t/s] 13: shit a brick!: An ejaculation. A variant is shit a million! (i.e., a million shits.).
1960		W. Styron Set This House on Fire 465: Shit a brick, how am I going to give him any blood?
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 17: Shit a brick, there’s fifteen and a zac on the clock already.
1968		D. O’Grady A Bottle of Sandwiches 89: Shit a bloody brick. Bloody dirty stinkin’ rotten bastard. [Ibid.] 206: ‘Shit a bloody pebble,’ he said.
1979		D. Maitland Breaking Out 125: Shit-a-brick, you only have to look twice at some of the blokes in that town to get thumped on the bloody head.
1984		P. Slabolepszy ‘Under the Oaks’ in Mooi Street (1994) 40: Shit a brick!
1986		P. Slabolepszy ‘Boo to the Moon’ in Mooi Street (1994) 91: spider: Fuck a Duck. jessica: Oh my God. What happened? [...] spider: Shit a brick.
1992		Sydney Morn. Herald 7 June 35/5: Fart a crowbar if the book didn’t go down quicker the the first cold tinnie at a butcher’s picnic.
1996		K. Lette Mad Cows 93: Shit a brick, Alex! Maddy panicked.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: shit a brick 1. interj. Exclamation of surprise. […].
2002		Sydney Morn. Herald 23 Jan. 18/1: ‘Ohhh, shit a f—ing brick. I have doing 60-second f—ing commercials’.
2003		McGill Reed Dict. of N.Z. Sl. 185: shit a brick!/shit a brick and fart a crowbar Extreme exclamation. ANZ c.1925. [...] shit a brick and build a house Exclamation, often at unexpected good luck.
2019		C. Hammer Silver [ebook] ‘Shit a brick,’ says Martin.
2021		C. Hammer Opal Country 308: ‘Shit a brick. Can you come back later?’.