Every now and then, a player at a showdown will slow roll. What this means is he’ll take forever to show his cards, even though he has the winning hand. He may even act like he lost but then displays a winner.
Slow rolling is very annoying…but it’s not illegal. The only thing you need to make sure is that you are not so convincing that the dealer mucks your cards. Then you’ll lose the hand because of your slowroll.
Otherwise, utilizing a slowroll every now and then is a good way to put your opponent on tilt…if you can manage to lower your self-respect enough to slowroll.