A simplistic tactic used by students in middle school and high school to attempt to startle and unnerve a teacher, especially a substitute teacher. Consists of an attempt to synchronously have everyone drop their books on the floor, usually synchronized by passing a note or by discussion the teacher's arrival.
The idea of a loud, military-grade thump seems frightening, but it tends to be thwarted by the students themselves. They are unable to actually drop their books simultaneously, instead producing a sort of cascade effect. This is because some of the students will use their watch; others will look at the various disagreeing clocks agree in the classroom.
In any case, I've never seen a teacher actually cowed by this tactic, yet it seems to be a perennial favorite, which makes me wonder if it's in 13 Ways to Sink a Sub.
I never thought much of this during my years in school, and in my honest opinion, if you're going to be immature in this way, at least get it right.