Double sit for fat people in airplane.

Maybe it's a little known fact, but the regulations of different airlines require that overweight travellers must to buy pre-emptively two places to be boarded.
Their size, in fact, makes them exceed the space reserved, causing inconvenience to the unlucky traveller seated on his side, as well as potential safety problems.
Lately, the uncomfortable inconvenient has caught the attention of many surfers on the net (and not only) because the passenger obligated to get off the plane just before the take-off was the movie director Kevin Smith (Mallrats, Clerks-Salespersons ). Once landed the bulky "passenger" has spread the news by Twitter.
Thousands of comments have been arising and the news has quickly become a national case forcing the Southwest airline to clarify its position.
What would have happened if it had occurred to an anonymous fat traveller?