I regularly teach the unreliability of witness statements in my job as a history professor. Somehow I've managed to do that for 15 years or more _without traumatizing any students_ with simulated shootings and armed robberies!
Honestly this Doonesbury cartoon works pretty well:
“While teaching a class to high school students on Wednesday, Burlington police officers staged a surprise demonstration in which a masked gunman burst into the room and pretended to open fire.”