If you study film, you know that entire texts have been written on the importance of "grounding" in a script.
The ground, also known as the glue, is the character that the viewer finds most relatable, most sympatico, when the story itself starts fray around the edges. Which is not to say that all scripts require a strong ground or glue, merely that the more outrageous scripts, the scripts with the least internal cohesion, require as much ground as they can get.
Which brings us to OFFICE XMAS PARTY, one of the more blatant examples of a "spaghetti on the wall" script. In other words, not a lot of fine tuning was done to get this baby ready for shooting day. The writers just took every gag they could think of, threw it against the wall, and then waited to see what stuck.
Some of it stuck, most did not.
But Bateman and Munn hold the film together by holding the attention of the viewer. In fact, they are so effortless at it that, every now and then, for just a split second, you almost think they are acting in another movie entirely, a romcom in which they are the only characters, and you are imagining the other 400 extras in this overdone extravaganza.
Is it funny? Not really. This reviewer laughed exactly once.
Is it engaging? Well, because of Bateman and Munn, actually it is.