I was just saying this two days ago to my girlfriend while we were sitting at a bar in a casino where I lit a cigarette: This place is the exact opposite of a hospital or an airport. I love this place because they want me to enjoy myself. I'm still under some kind of control, but unlike a hospital or airport, I'm not likely to die here, and as long as I'm within the boundaries of reasonable behaviour I probably won't even be assaulted. What I hate about airports and hospitals is that they now force you to relinquish total control over your own sphincters in order to be there; that, I think, is why so many people die in hospitals. The loss of control.
In attempting to regain that control, we drink; thus airport bars (and lounges and rewards cards).
Other than that: Flying causes gas. Drinking helps reduce it, and makes it less disgusting when everyone around you farts.