A kid comes home after school and hears noises coming from his parents bedroom and goes to investigate. Pushing the door open he finds his dad just going to town on his mom, that nasty kind of spread eagle sex, and his mom was screaming in pleasure.

He let out an audible gasp in astonishment and ran away.

Dad getting up, wrapped a towel around his waist and said "don't worry, I'll go talk to him"

Going downstairs, he hears noises coming from the kids room and opening the door finds the kid fucking his grandma. I mean really pounding her from behind when dad finds them. In horror he yells "what the hell is going on here?!?!"

And the kid turns and says "NOT SO FUNNY WHEN ITS YOUR MOM IS IT?!?!"