There are plenty, but one I'll always remember will be my first Instosis play.
Got the combo off nicely, since I always pay attention the first time I play a deck. Then for whatever reason it was, I dunno, but I did it like this.
Silu Dragon --> Mitosis --> 4x SoR
So I was alright, just needed the final blow. My opponent didn't even have a shield. But for whatever stupid reason, my final move was
Chimera --> Sky Blitz.
Lost the following turn.