Dog botherer!
(said to a preacher on hound kill)
Ogre : So the emperor is he a god or a man?
psyk: Thats a complex subject
Preacher: its not complex there are two answers the correct one and the one that gets you shot
and can we take a moment to appreciate the darkness of the medicae station…
Basically everything the Medicae Station says is my favorite line in the game! 
A line I have a lot of trouble with is the Preacher’s:
“Blood for the Emperor! Skulls for the Golden Throne!”
It feels like a clear reference to the quote “Blood for the Blood Good! Skulls for the Skull Throne!” but if you understand the lore you’ll know how completely inappropriate it is for a preacher to be making that sort of reference. 
Bugs me every time I hear it. 
Hadron: I can only imagine you attempted random inputs until it worked. But it is now working.
That’s my favorite line in the game! XD
“Dunno about this Astra Militaum thing, It’ll always be the guard to me.”
Clever mocking of GW renaming things so they can Trademark it.