There's a bit in Far Cry 2 where a guy is actually INSIDE a rock, with his limbs poking out. He can shoot at you still, but you cant always hit him, what with him being 'one' with an unshootable thing.
I also find it funny when the AI gets stuck in a corner and just faces a wall for a bit. You are wandering around, making loads of noise because you think everyone is dead, and you suddenly go "whoa! where did you come from?" as he continues to face the wall. Then you shoot him and laugh. Maniacally.

I also find it funny when the AI gets stuck in a corner and just faces a wall for a bit. You are wandering around, making loads of noise because you think everyone is dead, and you suddenly go "whoa! where did you come from?" as he continues to face the wall. Then you shoot him and laugh. Maniacally.