Should I be upset?

No, as he's showing you who he is. Because you'll only drive him away. I say this because Christmas is a pretty crap time of year for people his age. I'm sure if you think back you may remember. He's home for the holidays, so that means he's away maybe studying, he's used to his independence. This is also a time of self discovery. And he probably believes you guys will be there forever. Treat him like an adult. In doing so when he sobers up talk to him directly, ask him to spend time with you and the family. But you can't expect him to come home and stay there being bored especially if their are others he's not seen in a while. May seem selfish and in all honesty it is. But weren't you a little at that age?