Green’s Dictionary of Slang

rocker n.1

(Aus.) the mind, the brain.

[Aus]Truth (Sydney) 30 Mar. 11/5: He don’t drink himself. Not much, Sir, / [...] / For he wants a steady rocker. / On the game as he are at.

In phrases

off one’s rocker (also off one’s rock) [SE rocker, a rocking-chair]

1. crazy; occas. antithesis, on one’s rocker.

[Aus]Clipper (Hobart, Tas.) 1 May 6/2: She are goin off her rocker / With the howlin and the rant.
[UK]C. Rook Hooligan Nights 79: Wouldn’t a’e worried me off me rocker if they ’ad [seen me].
[UK]Eve. Teleg. (Dundee) 25 Nov. 3/3: Innumerable and curious euphemisms for ‘mad’ [...] ‘balmy in the crumpet’, [...] ‘a tile loose,’ ‘soft in the cocoa-nut,’ ‘off his rocker,’ ‘off his nut,’ ‘off his chump’ [and] ‘a little bit off the top’.
[UK]R. Tressell Ragged Trousered Philanthropists (1955) 595: The wouldn’t mind betting that ole Misery would finish up by going off his bloody rocker.
[Aus]F. Garrett diary 22 Oct. [Internet] Blue went away with a red label marked ‘concussion from bomb’ [..] and had gone quite off his rocker.
[UK]Boy’s Own Paper XL:2 76: I do not wish to see the book which has–has–has–sent Blundell ‘off his rocker’.
[UK]Wodehouse Inimitable Jeeves 66: So the Duke is off his rocker, what?
[UK]‘Leslie Charteris’ Enter the Saint 192: One of the men’s gone rather off his rocker and he was trying to chuck himself overboard.
[Aus]L. Glassop We Were the Rats 58: I think Margaret’s off her rocker.
[US]S. Bellow Augie March (1996) 143: It drove me a little crazy. I wasn’t right on my rocker anyway.
[Ire]J.P. Donleavy Ginger Man (1958) 256: I almost went right off my rock.
[UK]F. Norman Guntz 31: He just gave me this blank look as though I had gone right off my rocker.
[NZ]F. Sargeson ‘A Man of Good Will’ in Coll. Stories (1965) 140: Telling him he was clean off his rocker.
[US] in Woodward & Bernstein The Final Days 104: The next day Goldwater called Harlow. ‘Is the President off his rocker?’.
[Aus]B. Humphries Traveller’s Tool 44: Gwen sounded a bit off her rocker too.
[UK] in D. Campbell That Was Business, This Is Personal 21: I think he was beginning to go off his rocker with the life-style and the drink.
[US]Eminem ‘The Kids’ [lyrics] Stacey knew it was Bob and said knock it off / But Bob wouldn’t knock it off cause he’s crazy and off his rocker.
[UK]D. O’Donnell Locked Ward (2013) 223: A young woman was admitted [...] offer her rocker with a drug-induced psychosis.

2. (Aus.) drunk.

[Aus]Sydney Sportsman (Surry Hills, NSW) 3 July 1/6: For the missus she was shikkered — / Boozey — off her rocker — tight!

3. in fig. use, acting excessively (though not necessarily madly).

[US]‘Blackie’ Audett Rap Sheet 237: By that time I was practically off my rocker.
[UK]F. Norman Guntz 117: He is going to wind up going right off his rocker.
[Aus]T. Winton ‘Commission’ in Turning (2005) 224: Some of them [...] just drinking or going off their rockers.