Can't remember if this one's been told here or not, but here goes:

A man came home with a sheep in his arms and upon entering his house and seeing his wife said, "This is the pig that I have sex with when you are not available."

The man's shocked and disgusted wife said, "That's not a pig, it's a sheep!"

The man said, "I wasn't talking to you."

Bears, beets, Battlestar Galactica.