daughter (or student) has been using daddy's (her prof's) pipe to masturbate with
eventually her recognizes the strange taste.
What does he do about it?
I've got a story where a woman masturbates with her Barbie doll (several, actually), but using someone else's pipe IS a smokin' hot idea!
Maybe the prof wants to know who has been fucking his pipe, so he jerks off on it and leaves it out where it is easy to find. Then he waits to see who ends up in a family way.
Weed can make you hungry and horny. Two students smoke weed together, and one of them departues for snacks. The other one is horny and start masturbates with the pipe - until the first one is back and catches her.