What sign?
This gentleman is obviously breaking a sign on the wall, even though what he is doing doesn’t appear all that horrible. When travelers believe they have unrestricted control over the aircraft, flight attendants take offense. They are quite rigid about following the rules.
Yes, the passengers pay for the flight and the flight attendants are paid, but regulations are regulations. We wonder if the attendant truly woke this person up to advise them to put their feet down if they were asleep.