Before takeoff, one of the flight attendants asked the man to stow his tray table. He failed to answer, choosing instead to stare blankly ahead. When asked again and again if he was OK, the passenger failed to reply, failed to stow his tray table or to acknowledge me or any of the flight attendants who took turns trying to elicit a response. We became concerned about his fitness to fly; refusing to respond to crew instructions can result in a passenger being removed from the airplane.
That said, some passengers seem to believe the mandates don't apply to them.
I've worked flights from which passengers were removed for horrific body odor. I was involved in an incident in which pugnacious passengers were kicked off after a fistfight. I've seen passengers ousted for being drunk, unruly, high on drugs, low on morality and for wearing "offensive" clothing.
I've worked as a flight attendant for 35 years for one of the world's largest carriers, so I'm familiar with company policy. On numerous occasions I've had to cite chapter and verse when passengers refuse to obey the rules.