I'd have to say mine would be annihilating an entire enemy encampment (especially Fiends/Legion ), without being detected once (never says "DANGER" in Sneak mode), but saving one enemy that only can melee. After you get rid of every enemy but that one, just calmly walking into the open and standing there, then watching them run at you, and just as they lunge, blow their head off with a shotgun. Makes you feel like your probably the toughest guy to ever exist, but it's really easy.
My other favourite thing is the number of "WTF!?" glitches that there are. Like people getting stuck in the ground and such.
My other favourite thing is the number of "WTF!?" glitches that there are. Like people getting stuck in the ground and such.