From Halfie:
Voted Best Joke of the Year in Australia:

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

"Darling, this is the pig I have sex with when you have a
headache."

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

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