A principal of a small middle-school had a problem with a few of the older girls starting to use lipstick.
Though he was a rather stern disciplinarian and a bit of an old fuddy-duddy, he was not primarily concerned with issues of modesty and innocence. Rather, for some reason, when applying it in the bathroom they would press their lips to the mirror and leave lip prints, like so...
Before it got out of hand he thought of a way to stop it. He gathered all the girls together that wore lipstick and told them he wanted to meet with them in the ladies room at 2pm.
When they gathered at 2pm, they found the principal and the school janitor waiting for them.
The principal explained that it was becoming a problem for the janitor to clean the mirror every night.
He said he felt that the ladies did not fully understand just how much of a problem it was, and therefore he wanted them to witness just how hard it was to clean.
The janitor then demonstrated. He took a long brush on a handle out of a box. He then dipped the brush in the nearest toilet, moved to the mirror and proceeded to remove the lipstick.
That was the last day the girls pressed their lips on the mirror.