WTF Moment - Who's That Sleeping in the Bed?

I came home Saturday night from work and noticed a strange car in my driveway.  Nothing seemed out of the ordinary looking at the house so I figured it was my nephew in someone else's car.  I walked into the house and put my stuff down.  I walked to the bedroom to gather my work clothes for the next day.  I walked into the room and was greeted by the site of my sister-in-law and wife asleep in the bed.  WTF?  Did no one think it was important to let me know that we were going to have a house guest, even if only for one night?  Good thing I don't sleep in the bed with my wife.