At the end of the day, I have no problem whatsoever of some numb nut putting themselves at risk by getting out of their seat early (at my airline NO crew member is allowed to leave their seat unless there is a problem until the Pilots advices us to place doors in manual) and injuring themselves. What I do have a problem with is with said numb nut impacting onto another passenger or crew member should the aircraft make any jolts and injuring that person. I have seen the most horrific fractured skull as a result once before. I have a very firm (yet polite) PA which I make as soon as I see restless people start to stand up too soon and it always gets them back in their seats!