What's worse than sucking a dozen raw oysters out of your grandmother's cunt?
Putting in 12 and sucking out 13.
Grandma's Oysters
Explanation
Explain Bear
Alright listen up, nimrod. The joke is nasty. It's like, what's worse than imagining something super gross with your grandma? The punchline makes it even grosser. It implies something even more messed up happened. Like you, the joke isn't very smart.