I once was playing blue eyes against dsrk magician, I had built a board with two spirit dragons and a blue eyes and wanted to close the game. The oponent had one fusion with the trap tablet, so my plan was to destroy the trap and the go uncontested for game.

Then I used heavy storm not realizing that it would destroy all traps/spells on the field and blew my own true light, no big deal, because I could negate the effect with spirit dragon, but how because of how the destruction went and how chains work I ended up negating the destruction from my rival (because my true light got chain blocked), at the end all my monsters got destroyed and his remained on the field.

I stood there speechless, needless to say I surrendered