The Middle School was having trouble with all the girls who would kiss the restroom mirror after applying lipstick.  Warnings, announcements, occasional monitoring – nothing worked to break the habit, until the principal rounded up the likely offenders one day in the bathroom and explained that it took a great deal of work to clean the mirrors. “And to show you how much work it is, I have asked the custodian to demonstrate.”  At which point the janitor grabbed a toilet bowl brush out of the nearest stall and began to scrub the mirror.

The school did not have any more lipstick trouble after that.