Dean does as he's instructed – as per usual, having orders is the best thing for him (John knows it, which is why he's made sure things that should be instinctual are addressed that way, and Bobby knows it and takes advantage because it's when Dean's doing something that he's at his least guarded) – gamely chucking what he thinks is the right sort of quantities into the ground beef. He could just ask, of course, because really, he's got no idea, and guesswork might turn the mix completely inedible (to anyone who isn't Dean, that is, because he's pretty much a human-size trashcan when it comes to anything vaguely resembling food), but it's almost a matter of pride not to because seriously, how much of a charity case would that make him?
So when Jo turns back he's at the 'making patties' stage having thrown a bit of everything in with the meat and is bracing himself for her superior burger-making skills alerting her to some really obvious flaw like that they're the wrong colour or something, something any normal person who cooks normal meals in a normal kitchen would know but he doesn't because his burgers come dressed-up-pretty and ready to roll in polystyrene boxes and on crappy motel tellys everything always looks grey so his extensive education in daytime cooking shows doesn't help much either, and her Not bad takes him by surprise - seriously? - raised-eyebrow incredulity melting into a smug little grin.
> You do a lot of the cooking at home?
“No” he says – his tone says something else completely, says she's ridiculous for suggesting it, a yeah, sure, whatever. Get real, though not in an especially bitter way (the way Sam might have said it) which suggests he's somehow pissed off about the not-cooking, just one that says 'this is the way things are' - and something about Jo's pretty disarming, apparently, because he keeps talking while he works. Maybe it's the concussion, or the fact he's allergic to awkward silences, or wanting her to understand that their life doesn't suck all that much really as if he's anticipating an outbreak of unnecessary pity. “I mean, I used to, sure. Pretty much, uh, all of it really. But we kinda stopped staying places with kitchens about the time Sleeping Beauty there started 3rd grade.”