This is, essentially, the point of Gus Van Sant's film Elephant (Van Sant, 2003). Inspired by the Columbine massacre and other high school shootings, Elephant considers the question of why a teenager would one day murder a dozen of his classmates. The violence comes "out of the blue" (the opening and closing images are a blue sky) without warning or provocation. And Van Sant's suggestion is that the "elephant in the room" is that there is no explanation for the violence. This is just the kind of thing that happens in our world. Things are random and meaningless, hence the film's final lines: "Eeny, meeny, miny, moe..." The killers have no reason for what they do any more than anyone else does.
After the Columbine shooting, there was much speculation in the media about the causes of the killers' rampage. Was it the music they listened to or the video games they played? Was it their parents' fault? Were they bullied by their classmates? Elephant rejects those explanations. Each of the main characters has more reason to shoot up the school than the actual killers do. The other students have alcoholic parents, get punished unjustly by the principal, are made fun of by other students, are accidentally pregnant, etc. But only two of the students turn out to be homicidal. The fact that these students do murder their classmates is just as (and no more) inexplicable than the fact that the other students do not murder their classmates.
This inexplicability is mirrored in the film's camera work. Almost all of the film is shot in long tracking shots which follow students as they walk through the hallways of the school. This gives the film a restless, searching tone. But when the camera stops moving, something interesting happens. The camera stands still and lets the action happen around it without focusing on anything in particular. The best example is a scene on the football field early in the film.
The shot starts with the shy and nerdy girl Michelle staring unexplicably into the sky. She then walks off screen, but the camera doesn't follow her. The shot continues to show the field. In the background some students are playing football. They move on and off the screen, but the camera doesn't follow them. This continues for several minutes, an excruciating amount of time for nothing to happen in a movie. Since there is nothing to look at except the football game, we watch that, but the players keep disappearing. We feel that there must be something happening just off screen, but we can't see it. There must be more going on here that we don't know about. Finally a student in a lifeguard shirt walks by and we follow him into the school.
This feeling that there is more going on continues throughout the film. On screen, there is no plot, no story, nothing really happens. But we feel like there must be more going on than we can see, maybe off camera. The elephant in the room, however, is that there is nothing else. This is life as it is. This is life in its meaningless randomness. This is the nihilism of Elephant.