Dad: Son, I came back.
Son: Where is the milk?
Dad: Time for another 10 years.
Dad: Son, I came back.
Son: Where is the milk?
Dad: Time for another 10 years.
Okay, so basically, the dad left for milk but never came back...until now. But instead of bringing the milk, he's dipping out AGAIN for another decade. It's funny because it plays on the stereotype of dads who 'go out for milk' and never return. You probably think that's a good idea too, you're so dumb.