A certain college professor was notorious for getting off the topic of
the lecture, and on to his favorite subject: the evils of marijuana.
Off he went one day into his inventory of horrors, "Used regularly," he 
explained, "pot can cause psychic disorientation, sterility, cancer and 
castration!"
"Now wait a minute, professor," interrupted a student. "Castration?
That's absurd!"
"Yes young man, it's sadly true," replied the professor smugly. "Just 
suppose your girlfriend gets the munchies!"