You have to either vote on a bad SONG or vote on a bad PERFORMANCE. [...] Now, as long as we're talking about songs, I'd say my vote goes to Seasons in the Sun.
I guess you haven't heard Westlife's version, then, or you'd nominate it for the double. On the scale of egregious first-degree murderings of songs it's up there with The Presidents Of The USA's Video Killed The Radio Star and Wyclef's headmanglingly pointmissing Wish You Were Here.

As for really bad original songs, I feel your pain for Who Let The Dogs Out but would also suggest Daniel Bedingfield's saccharine stalkers' anthem If You're Not The One, the entire contents of the Now Christmas Album (not the new one, the old one that's played in a loop in every department store in Britain from September 1st to December 24th), and Snap's Rhythm Is A Dancer for, if nothing else, the sheer insanity of the couplet "You know I'm serious as cancer/When I say that rhythm is a dancer".

Peter