This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Core
The scene where they show the cabinet members exactly how the planet is going to get cooked by cosmic rays. Yikes.
The bird "attack" in London, which sends the city's commuters and tourists into complete panic. Some are covering their eyes as if they've been plucked out, while everyone is desperately evading the wayward traffic.
The destruction of the Golden Gate Bridge, as a tiny hole in the earth's layer caused one man's arm to instantly sunburn from being outside a car window. And then the bridge collapses in a way not unlike the Tacoma Narrows Bridge.
Worse still, those caught in the central span could not escape their cars, or they would've simply been fried instantaneously. Simply put, anyone still in the path of the effect had no means of escape.
The lightning-storm that destroys Rome's monuments and even statically charges coffee machines enough to cause a shock from touching them. Seeing such monuments like the Colosseum explode without crumbling is very creepy.
Project DESTINI. The idea of someone weaponizing earthquakes is a mercifully unrealistic prospect. It is ultimately the interference of DESTINI that triggers the entire crisis.
Iverson's death, where just when it seems they are in the clear to continue with their mission a random shard pierces his helmet, leaving a trail of blood on his face as his expression becomes an empty stare, before his lifeless body is consumed by magma.