I have asserted myself on a flight. A woman in the row infront of me was trying to open the overhead lockers while we were taxiing to terminal 4 at Heathrow so I demanded she sit herself down. I insisted a couple of times before making my feelings on her lack of inteligence pefectly clear to her and then the whole cabin. Of course being stupid she carried on emptying the overhead lockers of her stuff only to wait her turn to exit the plane like everyone else