There should be separate words for fake documentary films made for humour and fake documentary films made as pranks or for similar purposes. I'll lump in those made to show off video editing skills with that second group. Right now, the best word we have for them both is "mockumentary", and I don't feel that covers the second case very well.
Mokalus of Borg
PS - There's also "docufiction", but I struggle to see that one taking off.
PPS - Perhaps two words for such similar concepts would be confusing.