messing up my rook sac
What was your worst blunder? (we all make mistakes)

I've blundered mate-in one more times I can count. Probably the worst was I not only blundered mate-in-one, but I hung my Queen.

I've got to nominate mine in an OTB game a couple of weeks ago. I've got the black pieces in a local rapidplay league game. played at a 30-minute time control. White played 7.Bb5+. I was thinking, "Hmm, I want to develop my b8 knight to c6 eventually once other pieces are exchanged on d7, so I don't want to interpose with that; bringing the bishop back is a bit of a retrograde step, so maybe I would be better interposing with the f6 knight, which also threatens White's e5 knight. Okay, 7...Nfd7 it is."
8.Qxd5, Black resigns.

I once tried to sacrifice my rook so I could mate with my two bishops. I realized a bit too late that my rook being captured by his knight actually covered the square I needed the bishop to go to. The evaluation bar swiftly dropped from +5 to -6.
My opponent blundered a pretty hilarious stalemate though (he had two mates in one move, but decided to promote a pawn instead), so...I guess I'll take that.
Side note: He promoted the pawn to a queen. Promotion to a knight would have been checkmate. That just made it even funnier in my eyes.
Just curious to know what your silliest move was