Fallout 3.
I got the Victory Rifle and wanted to do some mutie-target practice in D.C.
I was snooping around in the trenches when i suddenly heard a yelp from Fawkes, I turned around to him promptly on the other side of the trench doing battle with his hammer, bashing his savage kinsman's skull to a pulp, I turned around to where I was facing before since it was obvious Fawkes was more than capable... only to find a seething mutie locking his arm high above his head, ready to grind me into a bone-marrow jelly, screaming "PUNY HUMAN!" in a raucous voice, and by reaction I shot off one bullet...
That .50 calibur miracle exploded from my rifle through smoke and gunpowder and planted itself right in the center that bastards skull, his eyeballs collapsed into themselves and came gushing out the back of his head, along with the rest of his skull, and just because its Fallout 3, his legs burtsed from under his hulking green torso which was covered in mesh and skull fragments, and launched 20 feet from where he was standing. I breathed a heavy sigh of relief, looted my kill, and hauled ass back to the citadel for some much overdue rest.
I f**king love that game so much...