The ad had read, How to avoid any legal charge short of mass murder; a five-minute class.

We all wandered into the classroom and sat down.  The teacher looked ordinary enough.  “Pick up your pencils, please,” he said.  We did.

“Let’s begin with how I will avoid a trespassing charge today, since I don’t actually have permission to be here.”  He paused, grinning.

“Okay, how?”  I asked.

“It’s easy.  For killing a room full of people using pencils smeared with fast-acting, skin-absorbed poison, I’ll be charged with mass-murder.  But I guarantee the authorities will overlook the trespassing.  See?  Guaranteed success!”