... and now per Continental's website so do they -

https://www.continental.com/web/en-U...2E95216E62680D

There was a discussion on the Continental board last week on this topic ("No room in the seat?") and apparently at least 1 FA is/was currently NOT aware of this policy.

The onus seems to be on the GA to prevent boarding of POS with only 1 seat:

" A customer is required to purchase an additional seat or upgrade if they do not meet one of the following criteria:

The customer must be able to properly attach, buckle and wear the seatbelt, with one extension* if necessary, whenever the seatbelt sign is illuminated or as instructed by a crew member.
The customer must be able to remain seated with the seat armrest(s) down for the entirety of the flight.
The customer must not significantly encroach upon the adjacent seating space. See our seat maps.
Continental Airlines will not board a customer who declines to purchase a ticket for an additional seat or upgrade for each leg of their itinerary when required." (bolding mine)

So not sure what other pax/FA can do once POS is boarded/seated.

ymmv