When a child in the family looks nothing like the father or siblings.
It implies that the mail-man is really the father of that child.
the mother is blonde and green eyed, the father is brunette and brown eyed, child 1 is brunette and green eyed, child 2 is blonde and brown eyed; however, little Bobby is a ginger.

People would say he has "mailman syndrome" or call the situation in general "mail-man syndrome"

It would be especially appropriate if the mail man was also a ginger.
by Your Mail Man January 18, 2010
Get the Mail-man syndrome mug.