Well I've been pulled off a plane (and replaced by an employee traveling on business) twice and been told to gather my things and move from 'first' to 'coach' (because of a late arrving pax) once. Trust me that walk from first to coach, carrying my little travel pillow, was one of the most watched 'boarding' of my life, with lots of pointing, quiet laughing and plenty of speculation on why I was being sent back to "take any seat" coach, just before takeoff.
By the time we reached cruising altitude, the popular consensus was that I was a coach pax who had tried to sneak into first class, a theory that was later reinforced when my meal was 'held ' until everyone else in the cabin was served. *Ah for the days of meals in coach*
One thing I can tell you, it's no fun being thought of as an inept crook who got caught even before the door closed.

Keep'em flying