I have a pretty high misery tolerance, so my list might be more properly titled "Good-To-Great Films That Will Be Very Difficult To Rewatch". A true list of films I could never watch again would be topped by "Date Movie", "Dukes of Hazzard", and Jenny McCarthy's "Dirty Love".
1. Salo, or the 120 Days of Sodom
--> I think this one is basically a masterpiece and it does exactly what it sets out to do. And what it sets out to do is make Power synonymous with rape, pedophilia, coprophilia, torture, and murder. The most thoroughly despairing film made by a country mile because all that despair feels like the perverted soul of every tyrant and narcissistic politician ever born. I spent a few days in a state of shell-shocked sorrow because I know the world's halls of power hold men with just as little regard for human life as the four leaders in this film.
--> Another brilliant film. The great David Bradley kicking off his long, great career with one of the all-time great child performances. It's one of the best social realist dramas ever made. Its glints of humor and joy and hope are like brief gasps of air for us and for a young English boy stuck in a bog of economic depression and family dysfunction. This life feels pretty drab. Then something incredibly cruel happens that is all the more brutal for how inevitable it feels. On a short list of most gutting endings ever and it just may belong at the top.
3. The Man Who Fell To Earth
--> I love Nicholas Roeg, even though this is probably one of his middle-tier films. It's a sci-fi picture with David Bowie as an extraterrestrial attempting to bring aid to his dying planet, while also getting caught up in all the trappings (and traps) of success on Earth. At a certain point cruel, violent, and horribly unfortunate things begin happening for Bowie's Thomas Newton and the people close to him. It's not Salo's kind of cruelty but the more casual horror of learning how flaws like greed, apathy, and depression can lead to terrible outcomes and leave us lost and drained.
4. The Donner Party
--> This is a fantastic documentary, made in the Ken Burns style by his brother Ric Burns. AV Club astutely called it "the most terrifying PBS special of all time". It's not just the infamous acts of cannibalism. It's the murder and the mistrust and the Aguirre-like sense of impending ruin that hangs over the expedition long before they even reach the mountains. And in a way all that aforementioned horror and hardship can't fully convey, it's how unspeakably ghostly it all is. The dry narrating style that made Ken Burns' "Civil War" academically rigorous somehow strikes notes of sorrow and menace when applied to this subject matter. It becomes an ideal method for conveying the terrible dread. Most chilling of all is that this grim, deathly document was routinely shown to fourth graders when I was young.
5. Requiem For A Dream
--> What can I say that hasn't already been said on this one? Aronofsky rains misery down on everyone with the aid of a weeping score and some terribly powerful imagery. Black, festering track marks. The demonic refrigerator. Lobotomies. Desperate, emaciated faces. Jennifer Connelly screaming her lungs out underwater like a banshee. Marlon Wayans' blood-soaked face and the smash cut to "Fall", which is less a season than the eternally damned state of the human soul. This goes all in on hopelessness. It could have felt like a maudlin PSA (maybe should have) but ends up feeling like the most apocalyptic chapter of the Bible. It's committed as all get-out to total devastation and I'm still mustering the stomach for a second viewing seven years later.