NDN is right. I can flip my cards on the table, the dealer acknowledges your hand and then you muck it. I've watched people muck their bb preflop. Dealers can't say ANYTHING to you about how to play your hand. Another way to screw up a hand, is to muck your hand onto an unprotected hand. Then both hands are mucked. That is why if you play live, ALWAYS, ALWAYS, ALWAYS cover your cards with a chip, dog, frog, or other trinket.