I would assume by this that they had quiet a large delay for takeoffs that day. I have never really seen major delays where aircraft are lined up along runways long enough for people to need to go potty.
How long had this particular plane been in line, and why are flight attendants letting people up when they are number 1 for takeoff. and did the captain come over and ashame that person to the entire cabin.
Here in aus we lock the lavs before pushback, and they stay locked until cruise.