It depends on when the all-in is called. If it's before the river, the person first to act (from where the button sits) is expected to show first. (If I'm not mistaken, somebody better versed in the rules of poker could answer this question better.) Also, if the all-in was called on the river, the person who was called is expected to show first. You can just sit there and be a douche with your hole cards in your hand for as long as you want to though.
Eventually you gotta flip'em face up and shout SEND IT! though.
I tend to do this for pots worth <$12 for dramatic effect. It turns heads in the card room if you can do it convincing enough every time.