It's amazing the judgement that can come out of four words. From, "I'm your worst nightmare," it has been inferred that this man walked onto that plane with the intent of disrupting someone else's flight. That he had flown before and knowingly only booked one ticket when he knew he needed two seats, thus making him an inconsiderate "fat slob." He's also clearly rude and selfish, as he wasn't the one standing.
Huh.
Alternatively: This man boarded the plane and was horrified when he realized how small the seats were. When his seat mate came, he apologized and tried to use self deprecating humor - hence the comment. As for standing, perhaps this man had a medical reason for sitting. There are a lot of health complications that come with obesity (no matter what the cause of obesity is). Or, as we don't know the story, the airline staff figured the other passenger would be less of a disturbance standing. (And before you dismiss that idea, how much intelligence have the staff shown so far?)