Passenger: I know the seat belt sign is on, but can I use the lavatory?I'm not sure, but I'm thinkin' that the flight attendant's response was not spontaneous and was carefully crafted by United's lawyers and carefully rehearsed by their flight attendants. I'm also wondering just how "grave" the danger could be given that the cabin crew was wandering around collecting trash.
Flight Attendant: Federal law prohibits that I answer your question with yes, though the cabin crew will not physically try to stop you. However, I must warn you that if you get up out of your seat you will put yourself and the other passengers in grave danger.
Nonetheless, the passenger chose to remain in his seat.