A player that lofts or flips their cards at the muck, without having called a bet, is bored or irritated with the cards they are receiving.
A player that just a lost a pot and did not have to show their cards, yet turns them up anyway, is showing the ‘beat’ they just took.
A player that keeps exposing a deuce or trey, without having called a bet, before folding is showing frustration with the cards they are receiving and mentally out of control.
A player showing a card, during the action, is trying to get a reaction from his opponents and see where he/she is in the hand. Keep in mind that in three or more way action, this move is completely taboo. And in some houses, even in heads-up action, your hand is dead if you show your cards before showdown.
A player exposing or flashing a card during play can actually hurt another player’s opportunity to benefit from having a big hand. And it can be a form of collusion. The reasons not to show your cards far outweigh the reasons to expose your cards.
Showing your cards should only be done for the following reasons: The first - to win the hand at showdown. The second - to show a bluff if you are trying to put a player on tilt. The third - to gather information from your opponent (but only in a heads-up situation). Showing your hand for any other reason is giving up information on your play.
If you are frustrated with the cards and the game, showing your cards is not going to change the situation. In truth, it only allows other players to ‘read’ where you are with the game. BEWARE! Exposing or showing cards is a giant mirror into what is going on with you during play.