For me, it's the Thousand Yard Stare by Thomas Lea. It's on the TV-Tropes page for, well, Thousand-Yard-Stares, and it freaked me out a little. I guess it had it's intended effect, because i'm pretty sure any soldier would be freaked out by someone who's been so profoundly affected by combat that their brain just disassociates emotionally and makes them stare out into space.