The Gunpowder Plot. Guy Fawkes and his friends were about to blow up parliament, and on the week it was supposed to happen, one of his accomplices sent a letter to a noble. In what was probably the worst example of "asking for a friend" in history, it asked "hypothetically, what would happen if someone went into the basement and blew up parliament". The noble did what nobody expected he would do and, get this, responded to the letter. People searched the palace basement and found Guy Fawkes, he was arrested and killed, and we have Guy Fawkes Day. The reason this led to a loss is because the king of England at the time used it as an excuse to persecute Catholics and make the holiday which is used as a taunt.
Guy Fawkes wasn't just killed though. He and his fellow conspirators suffered greatly before they died, and even after death their executioners inflicted torment on the corpses.
"They were to be "put to death halfway between heaven and earth as unworthy of both". Their genitals would be cut off and burnt before their eyes, and their bowels and hearts removed. They would then be decapitated, and the dismembered parts of their bodies displayed so that they might become "prey for the fowls of the air".