Green’s Dictionary of Slang

(US) exceptionally stupid or gullible; thus lopear n.

1845		W.T. Porter Big Bear of Arkansas (1847) 79: You sassy aig-sukkin’, roguish, gnatty, flop-eared varmint.
1846		Swell’s Night Guide 63: A thundering Turk – A lushy, sponging, lazy, lop-eared whelp.
1854		G.J. Whyte-Melville General Bounce (1891) 73: ‘Give me the pail, you lop-eared buffoon – do you call that the way to feed a pig?’ and the General, seizing the bucket from an astonished chaw-bacon, who [...] managed to spill the greater part of the contents over his own person and gaiters.
1876		‘Dan de Quille’ Big Bonanza (1947) 288: So this is the lop-eared cur of Calaveras who comes here to set up as a fighter?
1885		Bulletin (Sydney) 25 Apr. 18/1: Approved by the colonials generally means, of course, the approval of such flop-eared, hen-brained, nonentities as Sir Salmon Wilson and ’Enniker ’Eaton.
1890		Bush Advocate 13 Dec. 6/7: Knock-kneed, bow-legged, lop-eared. hump-backed, white livered, cross-eyed and so on .
1908		N.Z. Truth 3 Nov. 8/6: Guessing should be pretty brisk if some lop-eared son-of-a-gun doesn’t discover that this harmless [...] form of amusement isn’t contrary to the [...] Dead Dog Act.
1909		‘O. Henry’ Roads of Destiny 202: You blankety-blank, flop-eared, sheepheaded coyote.
1916		J. Lait ‘If a Party Meet a Party’ in Beef, Iron and Wine (1917) 97: Do I have to let a lop-eared chicken-chaser like this run me all over town and get away with it?
1927		Nichols & Tully Twenty Below Act I n.p.: You’re all a bunch o’ bums [...] Look at yourselves, you lop-eared mongrels!
1938		F. Anthony ‘Gus Tomlins’ in Me And Gus (1977) 101: If that lop-eared, sore-eyed mate of yours [...] would only come out of that hall.
1940		D. Maurer Big Con 59: He’s no lop-eared mark.
1941		A. Gurney Bluey & Curley 30 June [synd. cartoon strip] You lop-eared flat-foot!!
1944		J. Cary Horse’s Mouth (1948) 48: No good getting angry with the lopear.
1948		K. Amis Entry in St John’s College JCR Suggestions Book, Hilary Term in Leader (2000) 170: His writing is the product of LOP-EARED ANALITY.
1964		E. Shrake But Not For Love 72: A hypocrite and a thief with a sugar-gutted, floppy eared, Ivy League snot for a son.
1979		D. Maitland Breaking Out 169: You are a bloody lop-eared, snaggle-toothed, drippy faced, [...] pig-headed, fart-faced flip of a fucking galah!