I watched it on TV, late at night, as a kid. I remember barely being able to fall asleep out of fear, and I think it took a week for the effects of this movie to wear off. I'm older now and I've seen enough sad, scary and disrupting movies that it doesn't affect me anymore, but I'm pretty sure that if I tried to show it to my SO, I'd have my own Event Horizon right there in the apartment.

EDIT: I also had the "next time I'm picking the movie" moment after I took my then-girlfriend to see Prometheus. The TED2023 trailer looked so cool and I didn't realize it's a prequel to Alien...