A song murdered by someone.

Just about anything from Rod Stewart’s “Great American Songbook” series.  

@frogman  --  RS should have been charged with a crime for sure. 

There should be a law against anyone covering Unchained Melody. In fact, even though the live version linked to above is pretty amazing, I'd say that the only version that should ever be played or sung is the original studio version. It's perfect. 

I hate to say a bad word about these two, but:

Aretha covered the Beatle's Eleanor Rigby. I have it. Its pretty bad.

I also don't like Otis Redding's cover of I Can't Get No Satisfaction.

I do like Wilson Pickett's cover of Hey Jude with Dwayne Allman on guitar. Its a different song altogether which sometimes makes a cover okay.

Guns and Roses' version of McCartney's Live and Let Die.

I don't know if great songs can ever be murdered by a cover--they survive and the cover just makes one appreciate the artistry of the original artist even more.  I like almost all covers I hear of songs I like, but my least favorite form of covers, categorically speaking, involve opera singers doing operatic covers of popular songs.  I bought, and then only listened once, to Kiri Te Kanawa doing hits from "South Pacific;" it was funny, but not that funny that I wanted to hear it again.