[Neither Sam nor Dean seem particularly big on celebrating their birthdays. In Sam's case, it's understandable, given that he no doubt associates his birthday with so many horrible incidents.

Dean, on the other hand... it's difficult to say. Regardless of how he might behave on the outside, chances are that he would still appreciate the gesture from them.]

His birthday always comes right after the holidays, which here in Wonderland is... [Not a pleasant time, to say the least.]

We could all go eat at the diner. It's what he would most likely end up doing on his birthday back home. [If only because that was a normal part of his routine when on the job.]