With the idea of the demo and securing the cabin whilst at the gate here are my views on that.
The airline I work for as soon as the doors are closed we arm them for emergency situations, we then immediately do our demo and secure the cabin and sit down, on my last flight I only got home this morning, we did just that. we were all sitting at our stations wait to leave when a passenger gets up 'cause they need the toilet, and believe me no matter what we said they were going to go!! So at least when the aircraft is moving people seem more inclined to hold on to there bladder and bowel contents till we are in the air
Also the first airline I ever worked for after leaving the active runway the rear facing crew used to stand at there seats, still in a braced position if we stopped. I saw, I would say a 5-6 yr old jumping about on there seat, I headed down to say please sit the child down in case we have to stop suddenly, at that we braked really hard, I just managed to stay on my feet, holing on to the seat backs and the child hit the seat in front and slid down to the floor. I looked at the parent/guardian and just said that is the reason you need to stay seated! The child wasn't hurt, just shaken up and the parent tried to sue and failed!
Another bug bear of mine is turbulence...................I have had seat belts come on for turbulence and whilst checking seat belts had a PA from the flight deck for the crew to sit down for severe turbulence, when crew hear that we normally sit in the nearest seat. I sat in a passenger seat as it was vacant and fastened the belt, It got quite rough, then I was asked by the passenger next to me to move as SHE needed the toilet!!!!! The look on her face changed as we hit the next speed bump and she hit the overheads as she had already removed her seat belt!! She had a nasty bump and a bruise but was other wise OK But as other have said it just amazes me that people think these things are for everyone else but not them.
As crew when we ask people to remain seated there is normally a good reason for it