Michael Moore's "Bowling for Columbine" is supposedly a documentary (which by definition is objective and based on facts), but for a long time people have been pointing out its lies.
I have seen many sites describe the lies in the movie, but here is one of the most comprehensive pages I've come across:
http://www.hardylaw.net/Truth_About_Bowling.html.
And it's not like there were a couple innocent mistakes... there is deceitful editing, misrepresented quotes, bad math, omissions, false implications, and blatant lies.
The movie gets mentioned quite a bit on TFP, so I would particuarly like the fans of the movie to read this.