So Castiel loved, and obsessed over plaid shirts, but doesn't own any of his own. But Dean had many plaid shirts that Castiel decided to "borrow", whenever Castiel knew Dean was going to be out for a hunt, Castiel would take two of his plaids.
Dean never noticed that Castiel decided to take his plaids, as soon as Dean noticed Castiel was cuddled up with one of his plaids, and yes Dean was repaying Castiel for the whole sleeping-watching thing from when he was an Angel.
Dean closed the door to Castiel's room, and as he did that Sam had to appear with an eyebrow raised, which leads to Dean just shrugging. Sam walked past, as Dean sighed with a light blush on his cheeks, the blush came from Dean thinking about how good Cas would be half-dressed in one of his plaids after sex.
Great now Dean had a problem to go deal with, and so he did, Sam was having a beer when Castiel came down to the kitchen and whined. Sam looked up at Castiel, with an eyebrow raised, Sam knew of Castiel's age regressions but never thought he would be regressed in the open.
Dean watched Cas and sat down, which let Cas take the chance of curling up in Dean's lap, as Sam and Dean talked he held Cas. Cas made small happy noises, any time Dean played with his hair, which always lead dean to chuckle.