You know the ones I mean, the ones which utterly miss the point of the original, or re-imagine them to the point of extinction, or in fact so poison the original song that you can't ever listen to the original without recalling the abortion of the cover version. Cover versions that sap the joy and wonder and beauty from the songs.
I'd first like to nominate the cover version of Fairytale of New York perpetrated by Ronan Keating and someone else (I shan't google it, as I don't want to know who decided that being the other half in this duet would further their career). I've only half-heard it, while standing in a supermarket queue, but that was enough to form a judgement. They even changed the lines where Kirsty MacColl snarls "you're a bum, you're drunk" and shane MacGowan sneers back "You're an old slut on junk" etc etc to something unbelievably anodyne. Take a guess for yourself.
N.B. "So bad it's good" doesn't count. Shatner belongs in the other thread.