Dad: I heard an actor killed themselves with a knife. It was Reese something.
Mom: Witherspoon.
Dad: No, with a knife, you dummy!
Reese With A Knife
Explanation
Explain Bear
Alright, listen up, you chucklehead. The joke is that the dad is pretending he doesn't remember Reese Witherspoon's last name and instead says the actor killed themself "with a knife." It's a play on words because he's saying "with a knife" instead of "Witherspoon." Get it? I didn't think so, bonehead.