My intital rection was similar to Mona's - except without the laugh (Britney Spears??? OMG, where's the hurling smilie... even the toilet one doesn't truly sum up my feelings here)...
That said, I prefer not to focus on negatives so any music I don't like, just gets switched off... so I don't have any "worst covers" (except that again, I have to agree with Mona, Kylie's cover of "Locomotion" didn't improve one iota on the mauling it got at the hands of Little Eva (? or whoever it was did it in the days before I was born...)