To give the impression that you don’t have the winning hand such as pausing before revealing what you have or because you’re waiting to see the other player’s hands. If you don’t know if you have won the hand or not, then it’s not poor etiquette to expect other player’s to reveal their hands first when they’re first to act. But if you’re holding the nuts on the river and betting has been done, you should just table your hand.
Although slow rolling is highly frowned upon and is disrespectful we just had to show you this slowroll by a 96-year-old man at the WSOP Main Event.