Little Johnny walks in on his parents having sex and asks, "What are you doing?" His father says, "We're playing cards, and your mother is my wild card."
A week later, Little Johnny walks in on his father masturbating. He asks, "What are you doing?" His father says, "I'm playing cards." "Where's your wild card?" Johnny asks.
His father replies, "Son, you don't need one when you've got a good hand."