Use debacle to refer to a violent disaster or a great failure. If the flower gardens come toppling down during prom, strangling some students and tripping others, you might call the evening a debacle.
Debacle is often used to describe a military defeat. If your army retreats, that's one thing. If your army is outmaneuvered and ends up huddled in a valley, surrounded on all sides by the enemy, forced to sing 70s sitcom theme songs by their savage captors––that's a debacle. Debacle comes from French débâcler "to clear," from Middle French desbacler, from the prefix des- "completely, utterly" plus bacler "to block."
