Set during "My Bloody Valentine", 5x14.
As an angel of the Lord, Castiel had never felt this before. He required nothing to sustain himself, not sleep or air or water. But he felt it, gnawing away at him as though his insides were besieged by acid, clouding his normally focused mind with a desire he had never previously experienced.
He was hungry.
At first the knowledge of his weakness was intolerable; it made him irritable and irrationally impatient with himself and everyone he was forced to interact with. Then slowly, his mindset shifted. Why should he deny himself? What would be the victory in leaving this hunger to tear at his vessel, the cravings and pangs putting more strain on Jimmy's body?
So he gave in, and that first bite was a soothing balm for the burn in his stomach. The whole cheeseburger disappeared, faster than he thought it would. He wanted more immediately, and since he had broken already, decided to let his vessel have his way. White Castle didn't really need all those hundreds of tiny burgers. Jimmy needed them, Jimmy was starving for them, locked away inside his own body without sustenance for so long, and Castiel felt no need to deny him anymore. So he ate, and ate. One more was never enough, the desire refused to diminish. Castiel had developed a taste for the things, a guilty feeling of pleasure at the texture of the meat and cheese, an excitement in unwrapping them, something so new to the ancient being.
Soon enough he realized that it wasn't just burgers, it was red meat in general. While Dean and Sam were visiting the coroner to see the latest victim, Castiel was eating a 72 ounce challenge steak, and winning. Then he shocked the wait staff by ordering a second steak; they had never seen anyone eat so much. He hit every restaurant with a challenge steak in the country, and then zapped himself away before they could take his picture for their Wall of Fame.
Castiel's arrival was now signified by the rustle of a paper bag to accompany that of his wings, and the distinct aroma of hamburger grease lingered on the air long after his departure. After the third day of Castiel's newfound obsession, Dean stopped ordering bacon cheeseburgers.
Following their showdown with Famine, Castiel's hunger died out and Dean's aversion to his once favorite food diminished. But from then on, Castiel contemplated food as a recovered alcoholic does a fine whiskey. Tempting, but dangerous, and better for everyone if you stay away. With this in mind, Castiel began to avoid the Winchesters while they were eating.