I found this game,lost by Fischer,trying to win a dead-drawn game http://www.chessgames.com/perl/chessgame?gid=1044722
worst blunder in chapionship game?

Chigorin-Steinitz, last game of the match is clearly the worst blunder ever in a WC match.
Chigorin outplayed Steinitz in a king gambit reached a completely winning position, and then lost the game and the match by blundering a mate in one.
Fisher's mistake is not "a blunder" but rather a miscalculation. Of course he did see that the bishop is trapped, but he assumed he had enough moves to liberate it. He probably missed the move 32...h3 (not played) 33.Kg4 Bg1 34.Kxh3 Bxf2 35.Bd2, and the bishop is still trapped.
In general, miscalculations that lose the game are called "blunders".
Fisher's mistake is not "a blunder" but rather a miscalculation. Of course he did see that the bishop is trapped, but he assumed he had enough moves to liberate it. He probably missed the move 32...h3 (not played) 33.Kg4 Bg1 34.Kxh3 Bxf2 35.Bd2, and the bishop is still trapped.
In general, miscalculations that lose the game are called "blunders".
I'd rather believe an IM, if he's right too, well that helps. There is a big distinction. But ok...
Well, if appeals to authority are your bag, then GM Reuben Fine said something to the effect of "every beginning knows this is a blunder".
I grew up learning chess in the 70s, and it was considered a blunder back then.
With perfect play it is a draw after Bxh2??? I'm not sure where I've seen this or who said it but there is a study-like defence? Anyone knows something about it?
There is an old analysis, claiming a draw after 37...a6.
However, I never bothered to check it's correctness.
Here's a related ChessBase article:
http://en.chessbase.com/post/breaking-news-fischer-loses-first-game-to-spaky-in-reykjavik
As for the topic, it's hard to top Chigorin's 32.Bb4 in the game below.
Well, if appeals to authority are your bag, then GM Reuben Fine said something to the effect of "every beginning knows this is a blunder".
I grew up learning chess in the 70s, and it was considered a blunder back then.
Appeals to authority when authority is right? Yes, I do not have a problem with that. You seem to be the "I learnt it that way, it IS that way full stop". Good luck.
What I'm saying is that calling Fischer's Bh2 a "blunder" is not some new thing. When it happened, it was called a blunder by GMs and commentators at the time.
You act as if there is a "right" here, when all of this is subjective. However, the broad consensus then (and from Fischer himself), is that the game shifted from a probable draw to an inevitable loss after Bh2.
Just because Fischer was a chess genius and was attempting to make a win out of a draw does not change the effect of the move. He admitted that he miscalculated, and he lost the game as a result.

If I knew tha the game I posted would have caused all this debate,I would not have posted it.I think that is not important establish if it has been a blunder or a miscalculation...anyway Fischer lost the game.
I would been curious to know others blunders in chess worldchampionship,that is the original question of this topic...
Pardon me if this has been covered before but I was interested in what eveyone's opinion of the worst blunder in a championship match was? Naturally eveyone looks at the double blunder in game 6 of the recent match as one that stands out but I was thinking there must be bigger. Korchnoi's missed mate on move 55 on game 5 of the 78 match is the first that comes to mind for me. Any other nominations?