EDITED based on the first comment below... I read this story and this one scene is stuck in my head and I want to reread it, but I can't figure out what it's from. DEAN is a mess with post-hell trauma and SAM is trying to take care of him. Something sets DEAN off and they end up in a bar fight (maybe?) and then when a police officer shows up SAM recognizes that the officer is acting like he was in the military, so SAM makes it sound like DEAN fought in Iraq (?) and the officer keeps the bystanders away and lets SAM take care of DEAN.

FOUND! See comments.