A shoe on the door

A grandfather went to visit his college-aged grandson at the dorm.

Grandpa was astonished to find that his son was living a life of sin and corruption, as shown by the very high-heeled shoe nailed over the doorway.

“In my day,” grumbled Gramps, “we would hang a horse shoe over the door for luck and then study late into the night hoping to pass our classes.”

“But grandpa,” replied the grandson, “that IS a whore’s shoe!”