Here's a nice one:
My wife and I recently attended a party at which there were four other married couples. Various handshakes took place. No one shook hands with himself (or herself) or with his (or her) spouse, and no one shook hands with the anyone more then once.
After all the handshakes were over, I asked each person, including my wife, how many hands he (or she) had shaken. To my suprise each gave a different answer. How many hands did my wife shake?
I'm expecting to hear the 'QI obvious answer alarm' playing with this post but......8! Unless there were more than just the four other married couples at the party.