My mum is up in arms about that fact that she sat next to a (very) obese gentleman on her flight causing sufficient discomfort for her to grab the cabin jumpseat in cruise.
The flight was a fully-booked shorthaul flight with BA from Heathrow.
Few airlines are willing to go the distance which for instance Southwest does with their customer of size policy, what can you do in this situation when it becomes unbearable?
It is not a pleasant situation for both of them - the passenger or the large passenger. It is very uncomfortable for the passenger and totally embarrassing for the large guy. In addition to that, it is uncomfortable and embarrassing for the staff.
Unfortunately, there is no one single rule that applies here; each airline has its own policy regarding this.
If the large person's body is invading your space and you have noticed this during boarding, make sure to speak to one of the cabin crew members immediately. Make it their problem. You are paying for a seat and it is your right to get a full seat, not a part of one.
Remember, the only time you can report this case is on the ground. It is the perfect time for crew or ground staff to find another seat either for you or for the large person, or to find another solution in the case that there are no spare seats. Once the doors are closed and the plane is moving without you talking about it, you have given complicit agreement to this situation and no one can do much about it in most cases.
This depends on the airline. Some airlines make large people pay; some others upgrade large people to business or first class for free as a part of their services (the airline I work for does this if no two seats are available in economy class). You could get lucky and get moved to a higher class and leave your seat for the other passenger. Either way, your problem should be solved before the plane takes off.
This is an odd and embarrassing situation. Make sure to talk in private with the cabin crew to avoid embarrassing the sized passenger publicly. Depending on the airline, the sized passenger can be deplaned from the airplane or asked to pay for an extra seat. You may also be asked if you would like to wait for another flight! Anything is possible if no extra seats are available.
It's a health and safety issue. Depending on the airline and jurisdiction, they may have a legal duty to ensure you are not injured by being squashed up. A few years back a woman travelling with Virgin Atlantic received compensation for just such an injury, so most airlines are at least aware of the liability.
As Nean says, report it to the cabin crew. Don't be tempted to discuss it with the obese passenger, because even if they promise to try to keep from squashing you, they might fall asleep and do it anyway.
Find a different seat.
One way to do this is to bring cash. After you board, if you happen to be in a seat you don't like (e.g. because the person next to you is large), find a more preferable seat that seems to have a solo passenger in it, and make an attractive cash offer to the person who currently has that seat to switch with you. Be upfront with your reason for wanting to switch, as they will likely be suspicious otherwise.
