USPS

A few weeks ago I went to the Post Office to pick up a package. Much to my disappointment, it was simply a returned package my little sister had tried to mail out. She hadn't put any postage on it - strange methinks. So, I take the package to her and explain. She exclaims, "Those dummies at UPS! The postage is right there!"
I say, "Did you just say UPS?" (she confirms) "Then why did you take this package to the Post Office?"