This is Dean experiencing the effects of one of the Four Horsemen, Famine. This moment in context for you:
DEAN (to Castiel) So, what, you just happen to know he likes the cosmos at this place?
CASTIEL This place is a nexus of human reproduction. It’s exactly the kind of-(Castiel watches Dean put ketchup on his cheeseburger) -of garden the Cupid will come to— to pollinate.
(Dean puts his cheeseburger back down)
SAM Wait a minute. You’re not hungry?
DEAN No. What? I’m not hungry.
CASTIEL Then you’re not gonna finish that? (takes Dean’s cheeseburger.)( looking toward a couple at a table across the room) He’s here.
X- Transcript of My Bloody Valentine, 5.14
SAM I thought famine meant starvation, like as in, you know, food.
CASTIEL Yes. Absolutely. But not just food. I mean, everyone seems to be starving for something—Sex, attention, drugs, love…
DEAN Are you serious?
CASTIEL These make me…very happy.
DEAN How many is that?
CASTIEL I lost count. It’s in the low hundreds. What I don’t understand is…where is your hunger, Dean?
CASTIEL Well, slowly but surely, everyone in this town is falling prey to Famine, but so far, you seem unaffected.
DEAN Hey, when I want to drink, I drink. When I want sex, I go get it. Same goes for a sandwich or a fight.
CASTIEL So…you’re saying you’re just well-adjusted?
DEAN God, no. I’m just well-fed. Look there.
Dean IS affected by Famine. He is well fed, yes, but that does not leave him unaffected. Everyone, each person began craving what they did not allow themselves in their daily lives. Some people sex, others food, love, attention, whatever it is in their day to day life that they sacrifice for whatever reason… These people were craving it and seeking it fiercely.
Dean, however, seems to have his cravings dulled. He is, as he states, typically easy and quick to fulfill his own cravings. “When I want to drink, I drink. When I want sex, I go get it. Same goes for a sandwich or a fight.”
What Dean is experiencing as an effect of Famine is an absence of cravings. He is quite literally craving Abstinence. He is craving the loss of every craving he has ever fed.
"I’m well fed." He says.
Dean, honey, you are fasting.
This is the first meta on Dean’s “hunger” that I’ve read that I can get behind.