Now, I'd argue with the 'prissy princess' description, as we've seen him go unbothered by mud and gore many times over the course of the show, but for the sake of argument I'll let that go. What I'm interested in is this assumption that an interest in keeping a living space clean and tidy necessarily carries over into keeping your fridge clear of spoiled food. Because if you actually look at the interior of the fridge, it's spotless.
The issue they have isn't one of keeping the fridge clean, it's of actually eating the food it contains in a timely fashion--a different matter altogether. It's almost to be expected, really, given how frequently they run off on cases, and how they don't seem to do much (if anything) to prep the bunker before leaving each time. Quite likely every time they come back after a hunt, the entire contents of the fridge (which are apparently leftovers, beer, and milk) have gone bad again. Really, it's no surprise they still eat mostly take-out. It's gotta be a heck of a lot easier than trying to keep track of food supplies when they're constantly leaving for trips of a week or more.
And here's a facet of the original issue that no one talks about: maybe the food's not actually spoiled. Maybe Dean's simply the kind of prissy princess who's overly picky about the freshness of his food.
Anyhow, go check out the prompting post (linked above) and join in the fun. :D