http://www.guardian.co.uk/music/2009/dec/20/rage-against-machine-christmas-number-1
TL;DR .....Facebook group was made to make "Killing in the name" UK Christmas no1 as a protest against Simon Cowell and X Factor winners (the equivalent of American Idol) always being guaranteed the no1 spot.
Whilst it's not really the best song, the line "Fuck you I won't do what you tell me" is the main reason why it was chosen...and when the band were playing live on BBC Radio the presenters told them not to sing the explicit line, but in the spirit of the line itself, they did it anyway
Then based on downloads only, the song beat X Factor winner Joe McElderry's version of "The Climb" (a Miley Cyrus song ) by 50,000 sales to claim UK Christmas no1, and break two records in the process.
1 for - Biggest sales of a song in one week in UK Chart history
2 for - First song to top UK Chart based on downloads only
In UK history at least, the biggest chart upset ever