Seeds aka Seeds of Sin (1968) – Andy Milligan.

Along with fellow exploitation maestro Jack Hill's evergreen, darkly gag-laden Gothic grotesquery Spider Baby, Andy Milligan's skuzzball Gothica Seeds luridly remains a twisted, cruel, fascinatingly camp dissection of wickedly warped family values. Perhaps taking its cue from Hammer Horror's similarly skewed dabbling with hagsploitation, Seeds sordidly presents the precipitous decline of demented dipso matriarch Claris Manning (Maggie Rogers) during a majestically malign, ruthlessly mirthless Christmas family reunion. Like National Lampoons on weaponized DMT, the mercurial, maniacal Manning clan are a scintillatingly sinister troop of perversely scheming skells, and their nakedly sated lusts provide for oodles of rampant, sensationally skeevey WTFuckery!

Happily, at no point does Mr. Milligan approach verisimilitude, his debased caricatures of hyperbolic humanity are playfully distorted to the point of sublime absurdity. Like an especially brutally executed autopsy, Seeds is faintly taboo viewing, you know you really shouldn't, but you can't turn away, and, yet, deep, DEEP down, you fucking love it, and absolutely don't want it to stop! Seeds is a rabidly nihilistic anti-Forsyte Saga, luridly laden with additional vitriol, queasy incest, and biblical, downward-spiralling delirium. To any unmoved by Seeds of Sin, their funny bones must have fatally diminished to that of Stalin's conscience. A potently experiential work of agitprop exploitation, arguably in a league of its own, Seeds remains a mad, monochromatic, monolithically misanthropic midnight movie monstrosity.