Florence Foster Jenkins is generally regarded as the worst singer in history. You may not even recognize it in its present state, but this is the famous Queen of the Night aria (“Der Hölle Rache”) from “The Magic Flute”. It sounds more like an alley cat in transitional labour.
According to Wikipedia:
Despite her patent lack of ability, Jenkins apparently was firmly convinced of her greatness. She compared herself favorably to the renowned sopranos Frieda Hempel and Luisa Tetrazzini, and dismissed the abundant audience laughter during her performances as “professional jealousy.” She was aware of her critics, but never let them stand in her way: “People may say I can’t sing,” she said, “but no one can ever say I didn’t sing.”