This isn't something I've established clearly, but it's one of those things that creators know about their characters' backgrounds. You can see it in this Thanksgiving strip: Yoru and Ray drink wine, Scotty drinks beer, and Chris drinks water. Fun fact: this is also the strip where I decided that Yoru is a vegetarian.
I've always thought of Chris as fairly health-conscious. He's got a muscular build, and he hits the gym with Terry. Having him not drink was about taking care of his body, not a moral objection. So I decided that, for the good of the joke, he got talked into drinking and ended up hung over ONCE in my comic. You're welcome, Chris.
Rock on, guys, and never stop drawing.