Scary scenes in non horror films?

[Trevor]

Most of the scenes in The Crimson Rivers (2000)  



The interrogation scene in Gorky Park (1983)  



The dream sequence in Still of The Night (1982): yikes.

[Alex]

The torture scene with the dentist in Marathon Man.

[Trevor]

The torture scene with the dentist in Marathon Man.

I remember joking with my dentist about that on one visit: on my next visit, he - jokingly, I hope - asked me "Is it safe?" 

[Jim H]

The hobo scene in Mulholland Drive.

[BoyScoutKevin]

Here are a half dozen non-horror films that scared me.
There be spoilers below, so one may not read further.

Atomic Submarine
the 1st appearance of the Cyclops.

Finding Nemo
the 1st appearance of the skin diver rising up behind Nemo.

Have Rocket Will Travel
the flame spouting spider

Wait Until Dark
Alan Arkin leaping toward Audrey Hepburn across the darken kitchen.

8 Below
the leopard seal poking his head out of the orca carcass.
I knew this would happen, and it still made me jump.

2001 : Space Odyssey
the leopard leaping upon the ape.
My feet were moving, even if the rest of me was stuck to the seat.

[zombie no.one]

Large Marge head transformation scene in PEE WEE'S BIG ADVENTURE

[stine.greta]

This movie gave me a goosebump.

[The Burgomaster]

The torture scene with the dentist in Marathon Man.

I read the book before I saw the movie. The way it is described in the book is even more unsettling than what they showed on the screen.

[Fox Sake]

The death of Melliish in a hand-to-hand combat with a German soldier from "Saving Private Ryan"

it was disturbing/scary because you could actually hear Mellish beg the German not to stab him with the knife, but the soldier did so anyway.