Neanderthal

chump, loser, schlemiel (also shlemiel), turkey

slouch

airhead, birdbrain, blockhead, blunderer, bonehead, bubblehead, chowderhead, chucklehead, clodpoll (or clodpole), clot [British], cluck, clunk, cuddy (or cuddie) [British dialect], deadhead, dim bulb [slang], dimwit, dip, dodo, dolt, donkey, doofus [slang], dope, dork [slang], dullard, dumbbell, dumbhead, dum-dum, dummkopf, dummy, dunce, dunderhead, fathead, galoot [slang], gander, golem, goof, goon, half-wit, hammerhead, hardhead, idiot, ignoramus, imbecile, jackass, know-nothing, knucklehead, lamebrain, loggerhead [chiefly dialect], loon, lump, lunkhead, meathead, mome [archaic], moron, mug [chiefly British], mutt, natural, nimrod [slang], nincompoop, ninny, ninnyhammer, nit [chiefly British], nitwit, noddy, noodle, numskull (or numbskull), pinhead, prat [British], ratbag [chiefly Australian], saphead, schlub (also shlub) [slang], schnook [slang], simp, simpleton, stock, stupe, stupid, thickhead, turkey, woodenhead, yahoo, yo-yo

anthropoid, ape, beast, boor, brute, cad, churl, clown, creep, cretin, cur, heel, louse, skunk, snake, stinker, tyke (also tike) [chiefly British], villain

booby, fool, goose, loony (also looney), lunatic, madman, nut

featherbrain, scatterbrain

rascal, rogue, scamp

barbarian, heathen, primitive, savage

animal, beast, brute

boor, cad, churl, creep, cretin, cur, heel, jerk, louse, lout, swine