Green’s Dictionary of Slang

1. (orig. US, also cocoa, cocoa-box, koko) the head.

1838		J.C. Neal Charcoal Sketches (1865) 37: ‘Let go, watchy! – let go, my cauliflower! Your cocoa is very near a sledge-hammer. If it isn’t hard, it may get cracked.’ ‘Pooh! pooh! don’t be onasy, my darlint! – my cocoa is a corporation cocoa – it belongs to the city, and they’ll get me a new one.’.
1890		Road 24 May 8/1: What put that thought into your cocoa? [DA].
1900		A.H. Lewis ‘Mulberry Mary’ in Sandburrs 11: She [...] boins all d’air off her cocoa doin’ it.
1901		‘Hugh McHugh’ John Henry 53: Simply because a guy is a genius does he have to rush around with a mop on his koko, and butt into a public building every time he thinks in the open air?
1903		Ade ‘Hickey Boy and the Grip’ in In Babel 112: Me pushin’ up the lid, you know, an’ putting out the coco to get a little fresh air.
1906		S. Ford Shorty McCabe 284: It was a punky lid, all right, but it had saved a lot of wear on his koko.
1908		Bulletin (Sydney) 1 Oct. 20/1: The bug wheels swift are buzzing in / Our shattered cocoa-box; / For we are ‘off our pannikin’; / We’ve fairly ‘done our blocks’; / We’re ratty, touched, our brains are gone.
1908		Sporting Times 18 July 1/5: ‘My cocoa’s cold.’ ‘Well, put yer plurry hat on, then.’.
1915		Wodehouse Psmith Journalist (1993) 170: I’m de guy what’s goin’ to swat youse one on de coco.
1920		A. Baer ‘Bugs’ Baer 30 Dec. [synd. col.] The cop hangs a holly wreath on his riot Yulelog before he drums taps on the thug’s koko.
1925		Dos Passos Manhattan Transfer 37: He says Beat it you lousy wop, and cracks me on the coco with his nightstick.
1930		Pittsburgh Post-Gaz. (PA) 22 Mar. 17/1: You take the case of one former boxer who when he gets squiffed on home brew or Third Rail varnish is not allowed to talk like the ordinary fellow who gets squiffed because if he does the boys tap their domes [...] and recall the day that Charley White tapped him on the koko.
1934		G. & S. Lorimer Stag Line 167: Any guy with two eyes and a ripe coco can protect himself.
1944		J. Archibald ‘Skip Tracer Bullets’ in Popular Detective June 🌐 The betsy went off, and something grazed Willie’s coco.

2. (W.I.) a bump on the head.

1972

C.E. Palmer Wooing of Beppo Tate 45: He was swelling over the right eye and a few lumps which we called ‘cocoes’ had appeared on his forehead.