Not so funny when it's your mom...

One day little Johnny was passing his parents room he heard some noises. He peeks in the door and sees his dad fucking his mom from behind. His dad winks at him so he shuts the door and goes to his room. A while later Johnny's dad came to check on him to see if he was ok. When he opened the door to Johnny's room he saw that Johnny had his grandma bent over the dresser and was fucking her from behind. Dad yells, "What the hell are you doing son?" Johnny says, "It's not that funny when it's your mom, is it?"