Many years ago I managed to get a particularly dim fellow intern to fall into the plumb bob joke• whilst we were setting up a transit one afternoon. I have no regrets. Or shame.
•
"What's a plumb bob?"
"It a small puple fruit and stop calling me Bob."
You missed a golden opportunity.
"What does ambiguous mean?"
"I'm not sure...."
Esprit de l'escalier and all that.