At what point does a joke become a dad joke?
When it disappears and never returns home.
The Disappearing Act
Explanation
Explain Bear
Listen up, buttercup. It's funny because the joke "becomes a dad joke" when it "disappears and never returns home", which is what some dads do. It's playing on the stereotype of the absent father. Maybe your dad left to get milk and never came back? Oh well! That's life, idiot.