The mailman.

One day an elderly woman was babysitting her neighbor's little boy. "Have you seen our new mailman" she asked "he is very handsome". "Yes" answered the little boy,"he wears blue underwear". Startled the woman asked how the boy knew the color of the mailman's underwear. "Well one morning when I woke up early, the mailman was running down the hall pulling his pants and shirt back on". The woman then asked if he spoke to daddy about what he saw. "Yes I did, and he said that he would give me a new bike if I promised never to tell mommy about seeing the mailman".