Dad had mom bent over at the edge of the bed and is pounding it hard, doggie style. Junior walks in and sees this. Dad, without stopping, looks back at Junior, smiles and gives a wink. Junior closes the door and walk away.
When dad shot his load, he goes looking for Junior. Dad hears noises coming from Junior's room so he investigates. Dad found Junior pounding Grandma, doggie style. Dad screams, "Junior! Stop that!" Junior looks at dad and says, "It's not so funny when its YOUR mom, is it?"