FAA Regulation:
The boarding of a passenger who appears to be intoxicated is a violation of Section 121.575 of the Federal Aviation Regulations (FAR). a. Further, passenger non-compliance with Federal Aviation Administration (FAA) safety regulations may result in interference with a crewmembers duties.
I put the word "appears" in bold above because it is specifically written that way because a person doesn't have to be intoxicated but merely has to appear to be intoxicated to give personnel grounds to remove someone from a flight.
So once he was unresponsive and then remained non-compliant and the Capt. decided to go back to the gate. At that point chances were very good he was coming off that plane one way or another.
If this was made up by the flight attendants the other passengers would be saying as much and advocating for him to stay, those things didn't happen so that should tell you something.
Apparently he stripped to his underwear, the word "shorts" was used several times by the flight attendants but each time they clarified their meaning by saying underwear.
First Class is boarded first so he had ample time to prepare himself for the flight and get himself into compliance. This isn't a hard thing to do. When purchasing a ticket you enter into a contract with the airline and agree that you will abide by their rules and regulations if you decide to be non-compliant then you are on your own if a situation such as this escalates.
Bottom line is, all this person had to do was simply put on his damn seat belt! But he's too entitled for that so..... Looks to me like he F'ed around and found out....
Check 21:27 on the video the officer even says to the baggage clerk something like, "we had a situation where a passenger was severely intoxicated and had to be removed..."
The lessons here folks are: don't be an entitled jerk, and follow the crews directions. Do that, and this will never happen to you.
