ANY AI enemy from STALKER (unmodded).
C'mon, really? Sequence of direct hits from the limit of your sight, health drops, armour takes a beating, drop to crouch, drop the assailant with two headshots, think to yourself - "Shit, that rifle seems pretty good, i'll go loot it.." run over, loot corpse, only to find they've dropped their Makarov next to them.
A Makarov. A shitty single action pistol, that struggles to punch through paper when you use it, and that's not counting the goddamned recoil. How the hell were they dropping surgical sniper fire IN THE DARK from that thing?