I made a ruling on this very situation just the other day. There is one other consideration to keep in mind: are there other people in the hand, or is it heads-up? In a cash game, heads up, I would rule with perfect consistancy that exposing one or both of your hole cards to get a read is legal. However we must consider if another player is involved in the hand (either an all-in situation or still actively betting does not matter).

Exposing your cards when a player is all in and you are in side action is wrong (especially so in a tournament). You are exposing your cards either to induce a call or push a fold. If you are trying to induce a call you may be putting the all-in player's hand in peril moreso than before (that is what if they guy you are hoping calls can beat YOU - oops. That definately hurts the AI player if they can beat you but cannot beat your opponent).

The other consideration is if you have 3 active bettors. You are feeding at least one or the two players extra information giving them an unfair advantage over the 3rd player. ie: Player A bets, you (player B) expose a card and taunt. Player C now has information player A never had when making his bet. Even if you are acting last (A bets, B calls/raises then you expose a card and act) player A is at a disadvantage to B again. Other thoughts?