Digital watch reflections
Bright sunlight. Teacher's eyes. Reflections from the watch glass. Interrogation simulation. Yum yum.
written by an*nymo*s us*r, approved by Susan

Until you do it with a mirror to the umpire of a cricket match from one of the upstairs classrooms and the whole class gets detention.
written by Ju*ian B*rn*ll, approved by Susan

This requires some effort, but if a number of you can convince your parents that you need a pocket mirror for a class project (on the speed of light, or the science of reflections, or something like that), then you can faithfully reproduce the searchlights from a concentration camp.
If the lights land on anyone, in particular someone haplessly entering your class, you can then divide into two groups - one howling like an alarm, the other barking like guard dogs.
This will make the person entering the room feel as awkward as it is possible for humans to feel.
written by Ru*ert B*eheny, approved by Log