My Answer; The Exorcist.  

IT was pretty bad, because I saw it so young. Weirdly, I'm not afraid of clowns or anything, so no lasting trauma.

I was really sad when Old Yeller died in the movie of the same name.  Wouldn't be surprised if I actually cried.

Stayed up late watching it and then just before bed I thought I saw it coming down the street.  Was awake all night waiting for it to come down the hall and absorb me.  (shivers!)

I watched "Deep Throat" and was worried that I was going to someday have to stick my dick in a mouth full of teeth in order to make a girl cum.  I would wake up in the night from a scary dream about a girl severing my penis with her teeth.  Here I am 45 years later and the only blood that has been drawn were from two girls with braces.  

2nd one was the original "Alien", which was the most serious Industrial Weapons-grade Monster movie, when the exomorph was the surprise guest at the dinner table.  

Never wanted to go in the ocean after watching that movie.

...door and when she opens the door, she'll look like...

Yep, Jaws did the same thing to me. And I live just about a mile from the beach. (lol)

I'm not really sure why.  I think the fact that it was a true story was hard for me as a young kid.

Star Wars was my 1st movie theater experience.  Age 5.  Opening scene when Darth Vader walks through the cloud of smoke in the cut door opening freaked me out.  That's what the dark side of Star Wars has lost over the years.  Rest of the movie I loved and was excited.  But for weeks after I had nightmares about that Darth Vader scene

Event Horizon

That's almost exactly the mental image he conjures up in my mind when I read his posts.

A cock that big and a mustache was too much to try to live up to.  
It took me a long time to get over having a statistically average appendage.

Agree "Exorcist" of course, but Zuni Fetish Doll from "Trilogy of Terror" with Karen Black- that seriously fucked me up!

Summer of 42

OMG, I saw that when I was in the 6th grade, I balled my eyes out for about 2 days after he died in that movie. After that movie and I do it this day, any movie/show where an animal dies, I either FF thru that scene or skip the movie/show altogether.

I don't know what my older siblings were thinking taking a kid to see that movie. Violent nightmares ensued.  Nice tits on Michael's Sicilian bride though.

But when I saw it on TV as a kid I couldn't go to the ocean for over a year.