Originally Posted by Wally Bird

There is a Federal Aviation Regulation (121.575) under which no-one who appears intoxicated is supposed to be allowed to board. The airlines routinely ignore it unless as you say, you are roaring drunk and incapable of standing. Otherwise the gate agents just want to get rid of you, and putting you on the plane is the best way of doing so.

Alcohol dehydrates you; not a good plan if you're about to spend 9 hours on an airplane.