As The Onion AV Club states in their review of CSA: The Confederate States of America, mockumentaries are a dime a dozen these days, since all you need is a chyron generator and a handheld camera. That, and at least one person to pontificate self-importantly and fake-obliviously about something obviously unimportant/stupid/ridiculous.
If you have ever made a mockumentary and feel like hating yourself, cruise on over to YouTube and take your pick from dozens upon dozens of shitty mockumentaries full of horrible people.
Is my mockumentary any better than these, really? If you ask me, I'd say it's a little better, and I could try to justify that with a bunch of reasons I've made up, but the truth is I'm simply biased. Based on what we see on YouTube, mockumentaries are growing more terrible by the hour, and that shittiness has infected the entire genre to include films made before mockumentaries became shitty.
If your mockumentary is just a guy doing bad improv riffs as a weirdo with delusions of grandeur, then fuck you, you fail, and that includes me. At this point the whole idea of a mockumentary is so cheap and lame and formulaic that any good one has to really transcend the form. Here is a good starting rule: If your mockumentary is more than 50% talking head interviews, it sucks. You clearly have no movie, just a lot of videotape and an actor who thinks he's funnier than he is. Even 25% is too much, really. Rule 2: Your premise is not worth over ten minutes. No, shut up. It isn't. Really.
The Office is the greatest mockumentary ever. Maybe the only good mockumentary ever. Yes, David Brent fits the deluded guy mold, but as a character, he's much more complex than that, and so are the other characters. The Office is not just about how Brent is deluded, but how everybody is. Tim and Dawn are in denial too. The mockumentary device becomes crucial in highlighting the difference between the characters' feelings and the fronts that they present to the camera. It's a story that is enhanced by its storytelling device, rather than a stock device in search of a dumb joke to plug in. They even have the restraint to not use chyrons, because they know the show is good enough not to need them.