Teachers: Whenever there’s a school shooting, hide under the desk.
Students: Hiding under desk.
Shooter: Well, no one’s in here!
Alright, listen up, buttercup. The joke is about how teachers tell students to hide under their desks during a school shooting. But get this, the shooter waltzes in and is like, "Welp, nobody's here!" because everyone's playing hide-and-seek under the desks. It's funny because it shows how pointless that hiding strategy is and makes light of a very dark situation, which I know you are too familiar with.