Dean counters Sam's I'm not stupid face with a diluted version of John's patented don't push your luck kid which with his far less haggard and impenetrable features comes out as an eye-roll which will be droll in a few years with a pointed glare and furrowed brow tacked on the end. “Stop being gay Sam” - 'gay' being Dean's insult-of-choice of late - “You know how much shit I'll be in if Dad thinks I let you go out.”
Satisfied with the excuse, though, he unhooks the chain. Sam's probably right – Dad won't ask. He used to try, at least, to talk about what they'd done at school, to find somewhere on the motel wall to pin up Sam's lopsided scribbles and Dean's lurid paintings of firetrucks until the manager started yelling about holes in the plaster, but since he started spending more time away than with them (which Dean's totally taking as a complement, a recognition that he's old enough to look out for Sam like an adult would – the alternative is... uncomfortable) he's stopped. Probably because it's really boring, Dean reasons, especially if you spend all day shooting werewolves and stuff. He wouldn't want to hear about kid's stuff either.