My wife works for an Airline and has done so for many years and this is what she says on the matter.......The law is pretty clear as most cabin crew will know already as its in their training. It is illegal for any person who is intoxicated or under the influence of illegal drugs to be boarded onto a public carrier flight. Likewise it is illegal to become intoxicated or under the influence of drugs while on board a public flight, no matter short haul or long.
Many airlines are sensitive to people acting drunk on flights, and have trained their cabin crew and ground staff very well in the art of spotting and dealing with inebriated passengers. Disruptive behavior can result in those involved being constrained during the flight, or being arrested on landing. Further if sufficiently violent behavior is experienced the plane will make an unscheduled stop to have the alleged drunk arrested. In this case all extra expenses for the landing are on that person’s tab – so it is a very unwelcome addition to anyone’s hangover, wouldnt you agree?
So be drunk and act up on the plane, at your own peril. Otherwise stay in your seat, get sloshed or have as many drinks as the cabin crew serve to you and enjoy them......and your flight. :-)