Little Jimmy is walking by his parent's bedroom when he hears a lot of noise. He opens the door and sees his dad with his mum bent over the dressing table having sex. Dad looks at Little Jimmy and smiles, gives him a wink and motions for him to leave the room, so he does.
A few minutes later dad is walking past Little Jimmy's bedroom and hears a noise. He opens the door to see Little Jimmy with grandma bent over the dresser having sex. Little Jimmy looks at his dad (who is dumbstruck) and smiles, winks at him and says, "It's not so funny when it's YOUR mother, is it?"