I thought the "show one show all rule" was you couldn't show one player your hand and not the rest of the table. For example, I have the winning and you fold but flash me the cards as you muck them to show me what you had, but no one else could see the cards. Here the rule show one show all would kick in. Like wise in a casino I was playing at I saw something simliar. Two players left, one player bets all in and the other folds. The winning player flashes one card then mucks the hand towards the dealer. The dealer announces that he has to show that card to everyone and since the dealer can't tell which card it was, he turns them both over.