For whatever reason you can think of. Were the facts wrong? Was it just useless speculation? Was it just annoying to watch for some reason?
There's the obvious ALIENS DID EVERYTHING! from the History Channel that is the subject of a lot of mockery.
For me, it's surprisingly NOT the Titanic conspiracy documentaries, but one of the more informative ones. Titanic at 100: Mystery Solved
Apart from the annoying and presumptuous title, I cannot stand the narration and editing. It's also embarrassing to see people I respect taking part in this kind of sensationalist stuff.
EDIT[

I had forgotten about Expelled, actually. Saw bits and pieces of it and it just made me turn it off.
There's the obvious ALIENS DID EVERYTHING! from the History Channel that is the subject of a lot of mockery.
For me, it's surprisingly NOT the Titanic conspiracy documentaries, but one of the more informative ones. Titanic at 100: Mystery Solved
watch?v=Sqv-ZlPYlp0
Apart from the annoying and presumptuous title, I cannot stand the narration and editing. It's also embarrassing to see people I respect taking part in this kind of sensationalist stuff.
EDIT[
Funny you should mention this.Queen Michael said:Loose Change.
watch?v=saHs6J0OXVI
Here's the whole thing if you're desperately interested.Lightspeaker said:SNIP
watch?v=mGyyIJKEjeY
AwwmSomeone Depressing said:Aside from that, every single Titanic documentary
I had forgotten about Expelled, actually. Saw bits and pieces of it and it just made me turn it off.