A farmer walks into his bedroom with his wife in bed with a sheep under his arm and says, "This is the pig I'm fucking." She says, "You idiot, that's a sheep!" He says, "Shut up, I wasn't talking to you."
The Farmer, His Wife, and a Sheep
Explanation
Explain Bear
Listen up, dummy! The joke is that the farmer is telling his WIFE that she's the pig he's gonna... you know. He's not talking to the sheep, even though it looks like he is. Get it now? You're slower than a herd of turtles stampeding through peanut butter!