(This one is a little risque, but wonderful, nevertheless: this was apparently voted "Best Joke In Austraila in 2005".)

Charlie walks into his bedroom with a sheep under his arm and says:

"Darling, this is the pig I make love to when you have a headache."

His girlfriend is lying in bed and replies: "I think you'll find that's a sheep, you idiot."

Charlie says: "I think you'll find I wasn't talking to you."