"Playing Poker" joke

One day, a kid walks in on his brother and his girlfriend having sex. He
says, "What are you doing?" and his brother replies, "I'm playing poker
-- she's the queen and I'm the king. The boy leaves, not knowing any
better.
A week later, the boy walks in on his parents having sex and says, "Dad,
what are you doing?" and his father replies, "I'm playing poker -- she's
the queen and I'm the king" He leaves again, not knowing any better.
The next day, the boy's bother walks in on him masturbating and says,
"What are you doing?" and the kid says, "I'm playing poker." "Where's
the queen?" his brother asks, and the kid replies, "What do I need a
queen when I've got a hand like this?"