For me it was "Human centipede". Honestly it wasn't the most traumatizing movie I've ever watched. But it did leave some type of mental scar. I can't ever look at a centipede the same.
As far as childhood trauma goes it was this horror movie about some possessed elevator that killed people. And no it wasn't Devil. I don't remember the name but I remember the kills vividly where the elevator killed a blind man and his dog, a kid, and another guy that it shot through the roof of the business building.
incident in ghostland i think its called?? it upset me for personal reasons but also its so fucked when movies dint even try, they just use triggering things to try and do shit any nothing else. its all shock horror and its the laziest shittiest kind. was forced to watch it. twice. was awful.