Well...Anyone "can" "demand" anything, you know. In fact, I picked that specific example because one of my mom's professors put, as a question on a final exam, that they were supposed to put a paper bag on their head and cluck like a chicken. (It was the 60s.) Whether anyone actually did so or not, I don't remember now. But I do know that each time I board an aircraft, we're told that we have to comply with "all" crew member instructions. No mention is made that we have the option to decline ridiculous crew member instructions -- although we'll hope that the issue is never tested in the real world, since there's a limit to what an FA would "demand" you to do without themselves feeling ridiculous. I could see it as a practical joke on Southwest back in the 80s.