Rocks fall, everyone dies
This was used in the ending of the NWN2 original campaign. And at the beginning of the first Icewind Dale game, killing everyone that isn't the player party. In theory, this may have been inspired by Tomb of Horrors, in which entering the wrong room CAN lead to "Rocks Fall" everyone dies... if you don't leave within 10 seconds.
Another variant on this, used as a tactical strike against That Guy, is the "Rocks fall, you die. Everyone else levels up." as in D&D players can earn XP from witnessing events that no one has ever seen before. So you bullshit the players with a story about how magic is created by meteorites of pure magic falling through the atmosphere and as they burn up the microscopic dust suffuses everything and creates magic.
So players are walking along, one player is being a cock, magical rocks scream out of the sky and flatten them and due to the beauty and amazement of seeing something like that everyone else in the party levels up.
Might also refer to the Orkish tradition of using hollowed-out asteroids, coated in guns and filled with orks, to be hurtled from SPACE and thrown onto a battlefield on the planet below. The resulting collision (if it hits anywhere near its intended target) will kill lots of enemies and cause the surviving orks to pour out and kill everyone in sight. TV Tropes also considers this an appropriate saying for any cheap bastard who's performing orbital bombardment with kinetic weaponry. Like rocks.
But most probably originated in previous versions of D&D, where there was no Save vs Rocks Fall.