Great Moments in Roleplaying: Describe the moment when the player/s realized how f@#ked they really were. A player said to a Daemon, "I'll do whatever you want, I just need that information" and then tried to back track once I said "You said what?". Needless to say two other party members nearly died from that.

When my assassin is crawling to the site of detonations, and see Flesh Tearers fallen from the Black Rage/Red Thirst killing one of the and preparing to rampage.

He just **** himself and made him so slow, while a space marine smelled him.

A Rogue Trader GM here, it happened several times in my campaign so far that the party found themselves ill-prepared or out of their depth though the one that stands out to me was during a Beast Hunt on the planet of Burnscour.

They went down with a force of around 30 men and had armed their troops with heavy shotguns loaded with Stun Shells and Snare Grenades, in the hopes that they would catch their prey alive. As they approached the site of a shuttle crash which they had been told was a nesting ground for "large predators", the mercenary guide they had hired began to look around at the foliage. He told them they were being stalked, and that they should make their peace with the Emperor. The sound of silence that followed after this hardened merc, that I had been RPing the whole session as this brash, uncouth, and arrogant man, began a solemn prayer of protection was fantastic.

Suffice to say they succeeded in their hunt, bringing back 3 mostly-intact bodies... and leaving about a dozen or so men dead on the surface.

A player boarding a rogue trader's starship fired a suppressive burst across a compartment hatch, unslung a belt of frag grenades, hurled it through and slammed the hatch closed.

At which point he saw the warning sign on the hatch that the compartment beyond was the gun deck's munitorium.

When we discover the part we need to salvage from the Warp-Tainted space station is integral to the Gellar Field keeping the place from going full Chaos. That said, we NEED this piece or we will die.

The following encounter/screaming escape from the space station killed one PC and caused another to burn a Fate Point (he had to get a new Bionic Heart and Respiratory System when we got him to the medicae bay on the ship we had to repair). Insanity for everybody! Corruption for most!

When my old DH1 group finally tracked a cult leader to his lair only to find him being possessed by a daemon. Half the group panicked and ran away... Then the Guard mechanic returned, fired his lasgun and made something like 4-5 Righteous Fury rolls (they were funny back then) and killed the thing outright.

Or facing the Dancer in that included adventure from DH1. That has wiped more groups than I can count (until one very lucky/brave Acolyte ran up and gouged the eyes of the thing with his thumbs).