One day little Johnny heard a noise and peeked into his parents room to check it out

One day little Johnny heard a noise and peeked into his parents room to check it out.
He opened the door to see his mom bent over the dresser and dad going at it behind her. Johnny's dad saw him and gave him a little wink as Johnny closed the door.
After business was finished Dad went to check on little Johnny. He opened his bedroom door to find Grandma bent over the dresser and little Johnny going at it behind her. Dad yelled, 'Johnny, what the hell are you doing?!' Little Johnny replied, 'It's not so funny when its your mom, is it?!'