eves dropper 

One that lurks about to rob hen-roosts; also a listener at doors and windows, to hear private conversation.

My father always plays the eves dropper every time my boyfriend comes to my house.

eves dropper by Jamie Barteldes July 2, 2008

eavesdropper 

Listening "in the wings" to other people's private conversations.

She's such an eavesdropper, you can't say anything private with her in the house.

eavesdropper by Kenny W. December 19, 2007