Shania was bad, Tori Amos worse but Celine Dion gets my vote. Absolutely the worst, most cringeworthy effort I think I've ever seen from a so-called superstar. She should stick to her usual brand of mundane, puke-making ballads.
All-time worst covers lifetime award must go to Westlife though. For over a decade they have consistently produced more appalling covers than any other band I can think of. Well done boys, takes real talent to karaoke other people's songs. But fair play to them, they've made a lot of money out of it.