Chess is a game of the mind, it requires planning a method of attack in order to secure a king, which means that your opponents state of mind comes into play.
By gloating during play; a player accedes his mental position to you. He gives away that state of mind that gives you an edge. He may think he has an edge, even if he does have an edge that doesn't mean he has won.
A player has not won until the enemy king stands in check mate, if a person is gloating, they may think the game is over before it is. They may also be trying to invoke a second mind game above the initial mind game of chess. Distracting your focus from beating him towards thinking of comebacks to his remarks.
To illustrate my point I will use one of my more experimental games.
During a ranked match against j___miah I was probing for a possible check mate strategy against an opponent who was capable of countering whilst putting me at a disadvantage, literally tearing into me until I had very little left on the board.
At this stage in the game I thought I was done for.
So what could I do to recover this dire scenario.
I was 17 points down against his 4 points of damage.
Just a queen, two rooks and 3 pawns were all that stood in the way of a loss.
A lot of people in that position might be inclined to resign but I was focused on trying to win with a risky strategy and here is how it played out.
I must admit I wasn't playing well at all, I blunder often and the win was mostly down to the other player not spotting the obvious but a win is a win.
If he had been more focused on the threat at his back he might have won, if he had spotted the fork on the queen he would have won.
In short, don't let them shake you, you never know what you might get away with.
@fhwee you played with an animal that happened to be versed in chess. block the creature after the game.
I'm playing with one myself now. He's ranting away non-stop ever since the beginning of the game, in quite incorrigibly third rate expressions...
http://www.chess.com/echess/game.html?id=49927585