I've overlooked quite a few Mate in 1's where I was far ahead in material.
Blunder!
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My worst. For some reason I though she'd play Bf8 and just didn't notice that she didn't:
http://www.chess.com/echess/game?id=63485726
What's your biggest blunder. I've just played a game I was about to win, and wanted to suggest resign to my opponent.But I clicked the resign button, and lost 11 points!