I was curious, if you do like a monster bluff in hold em' and your hand is literally the board, someone calls you and its time to show your cards. Do you legally have to show your cards in this case, or can you simply say, my hand is the board and muck your cards?
The short answer is yes, always. Most poker rooms and rule books state plainly that you must table your cards face up to have any claim to a pot. Tabling your cards means placing them face up on the table, so that all players can see them. If you say my hand is the board and muck your cards your hand is dead and you will have no claim on the pot.