Green’s Dictionary of Slang

holy mackerel! excl.

also holy mac!

an excl. of surprise, shock, wonder or amazement.

[US]S. Crane in N.Y. Press 20 May in Stallman (1966) 55: ‘Hully mack’rel,’ said Billie, ’I’ll never it t’ Omaha.’.
[US]‘Hugh McHugh’ Beat It 33: Holy mackerel! I’d like to see you travel over this part of the universe.
[US]H.C. Witwer Smile A Minute 300: ‘Holy Mackerel!’ says Frank, pale as milk, ‘it must of slipped outa my hand!’.
[US]H.C. Witwer Fighting Blood 253: ‘Holy mackerel,’ whispers Nate, ‘you’re lit up like a church!’.
[US]J. Lait Broadway Melody 40: Holy mack’rel — the biggest day o’ her young life, an’ she’s got the weeps.
[UK]W. Watson Miss Pettigrew Lives For A Day (2000) 115: Holy suffering mackerel! Where are we now?
[US]B. Cerf Anything For a Laugh 11: ‘Holy Mackerel,’ exclaimed the soldier.
Wash Tubbs [synd. comic strip] Holy mackerel, Louie! We gotta stop that guy.
[Aus]T.A.G. Hungerford Riverslake 248: Holy mackerel, he’s in a hurry!
I. Fleming Diamonds are Forever (1965) 163: Holy mackerel! Just any old dumb hag who can cook and lie on her back?
[US]E. De Roo Young Wolves 98: Holy Mackerel, that’s ambrosia!
[Aus]D. Niland Gold in the Streets (1966) 90: Holy mac, everything happens to me.
[Aus]‘Nino Culotta’ Cop This Lot 51: Joe looked very startled. ‘Holy mackerel,’ he said.
[UK]R.L. Pike Mute Witness (1997) 43: Holy Mac, Lieutenant; what will Chalmers say?
[UK]C. Stead Cotters’ England (1980) 76: Someone opened the front door. ‘Holy Mackerel, what time is it? Is that Nellie?’.
[US]‘Iceberg Slim’ Pimp 137: Holy mackul, boys. You smell dat?
[US]L. Rosten Dear ‘Herm’ 298: All I can say is Holy Mackeral.
[Aus]N. Keesing Lily on the Dustbin 24: Women used to let off steam domestically with a fine range of substitute expletives. ‘Holy Moses!’, ‘Holy mackerel!’, ‘great balls of fire’, ‘good gravy’, ’jumping Jehosaphat’ and ‘muddy great buckets of pitch’.
[Aus]Penguin Bk of More Aus. Jokes 382: Holy Mackerel, look at all them fucking Kooris!
[UK]Indep. Rev. 2 May 7: Holy mackerel, he is going to pedestrianise the centre of London.