The first time I ever watched Trainspotting (like a decade or so ago) I had taken 2 tabs of acid and looked up online "movies that will change your life" or something along those lines.

One of the first ones listed was this one called Trainspotting and I had no idea what it was about I was expecting some drama about a special needs little boy who likes to look at trains or something.

Ohhh boy. That one scene was horrifying I got up and almost turned the TV off but I'm glad I didn't. I love that movie so much.

Requiem for a Dream. You're absolutely correct, a one-time-only must-watch. I always enjoyed re-watching films with friends, but this one is a no go. One thousand years ago, I added the DVD release to my collection on release. Where I grew up, our movie theater only carried ultra-mainstream titles, so when films like Requiem released to theaters, it was either a 2+ hour trek to the nearest metropolitan area or just wait for it to release on DVD. I could be misremembering, but I believe the DVD case was one of those awful cardboard cases with the plastic clip. Anyway, it was mixed in with the rest of the DVD collection I proudly displayed in my living room (we all did this). At least until I had to refuse requested viewing by different guests not once, but twice. Fortunately, somewhere around that same time, I pumped the brakes on tangible media, and started gathering digital rips. Packed all that valueless stuff up, and shoved it up in the attic.

Changling is another, the A. Jolie kidnapping flick