Green’s Dictionary of Slang

sap-head n.

a fool.

1798		T.G. Fessenden ‘Political Pepper-Pot’ Poems (1804) 61: The poet, nimbly, trips it back / Over the Union courses rapid, / And squibs each Jacobinick saphead.
1828		W. Carr Dialect of Craven II 96: Sap-Head. A blockhead.
1842		Whip & Satirist of NY & Brooklyn (NY) 3 Sept. n.p.: the whip wants to know Whether those two sap-heads [...] had an idea .
1848		Southern Reporter (Cork) 20 July 1/2: ‘O you tarnal sap-heads, you green-tailed lizards, why don’t you come along and pay for your paper?’.
1859		T.F. Upson diary Mar. in Winther With Sherman to the Sea (1958) 4: Then he said, ‘you are sap heads’.
1861		N.E. Police Gaz. (Boston, MA) 12 Oct. 6/4: Who isthe biggest saphead on Middlesex street?
1862		Preston Chron. 1 Mar. 4/1: He was promoted to the captaincy of a regular squadof sapheads.
1873		J. O’Connor Wanderings of a Vagabond 43: I have had sense enough to catch you dealing from the bottom on those sap-heads up there.
1879		Aberden Eve. News 4 Sept. 4/4: ‘The sap-head, the shallow pate, the crazy, crack-brained imbecile’.
1880		H.L. Williams Darkey Sleep-Walker 4: Ky, what a saphead!
1894		Eve. Teleg. (London) 20 Feb. 4/3: I don’t see how you can laugh at saphead’s insane jokes.
1894		Truth (Sydney) 8 Apr. 4/8: ‘Sykes,’ with a ‘y,’ as our daily paper sap-heads persist in spelling it.
1904		G.D. Chase ‘Cape Cod Dialect’ in DN II:vi 427: saphead, n. A weak-minded person.
1904		Sun. Times (Perth) 20 Nov. 1/1: Saphead Simpson and Bounding Bold ought to put their flurried pates in ice-packs.
1904		Derby Dly Teleg. (UK) 11 Aug. 2/5: Big Brother: ‘I should like to know what you’ve been flirting with that Saphead for?’ Pretty Sister (indignantly): ‘I haven’t’.
1911		G. Stratton-Porter Harvester 559: ‘What an old sap-head I am!’ she commented.
1918		R. Lardner Treat ’Em Rough 140: A corporal has got to keep going and try to keep his men going and when you got a bunch of sap heads like mine it keeps a man on the jump to tend to them.
1925		Dos Passos Manhattan Transfer 151: It’s stage money ye simple saphead, you goddam.
1936		J.T. Farrell World I Never Made 125: You saphead, God made everything.
1940		E. Curry Hysterical Hist. of Aus. 83: Now, my sweet sapheads.
1958		(con. WWII) F.I. Gwaltney Heaven and Hell 2321: Miles must’ve been more of a saphead in those days.
1962		(con. WWII) J.O. Killens And Then We Heard The Thunder (1964) 17: You little sawed-off stupid-talking sapsucker.
1981		P. Reading ‘The Euphemisms’ Tom O’Bedlam’s Beauties 42: Addle/Silly/Chuckle/Dunder / Sap/Bone/Block/Thick/Muddle/Crack- / Heads.
1981		C. Hope Separate Development 189: Saphead [...] they’re not allowed on Sunday.