While traditional sitcoms typically unabashedly outrageous humor, mocumentary has made the banal funny. The office focuses on an exceedingly drab workplace an almost tragically uneventful town. Ironically what is initially unrealistic about the premise of the show is that a documentary crew would think to film something so seemingly realistic.
The pervasive realism throughout the show makes for much of the humor in it. Many of the jokes are derived from the characters being awkward and clumsy. Physically or metaphorically stumbling throughout their days, in small and large ways. In Gay Witch Hunt, Michel's catastrophic actions are so painful to watch because they feel so real. Each time he makes a point to his boss about the gay community he turns back to the camera in a "am I right" gesture. Only the gesture is a little off, facing just to the left frame. It's gut wrenchingly awkward and hilarious. Character weirdness is present in the small things during the show as well. For whatever reason the shot of Dwight shredding a business card in the intro is particularly evocative. You almost begin to ask why he is shredding a business card, but don't because it seems like too small of a thing to devote any sort of energy to. I would argue that character weirdness is what makes a lot of the realism in the show. Most people are idiosyncratic to one degree or another.
This is not to say that The Office, or any other mocumentary, never becomes whimsical. At the end of Gay Witch Hunt Jim convinces Dwight that he has made an actual gaydar. In a later episode Dwight builds dozens of snowmen in an incredibly short amount of time. This moments feel real, however. Maybe it is because they are shot so much like a documentary would be, or it could just be the style of acting. So much of traditional sitcom acting (or from what I've seen of it) is pushed and theatrical, whereas mocumentelivison is downplayed and conversational. Mumbles over projection. Even in the locked down interviews the character's dialogue feels a little confused, a little delusional, very real.