Edited 7/31 - thanks Zeb:
Aparently, the video was removed from tou tube. Let me try to explain it, and it won't be nearly as funny.
The video is captioned 'Cyber Sex'. Boy is sitting in front of his computer IMing a girl. They agree to have cyber sex. He is watching a video of her pulling her shirt up. He stands up to drop his drawers, when he is called down to dinner by his mother. Boy starts to eat dinner, scooping mashed potatoes onto his plate. His sister is sitting across from him. He looks over at her and realizes that is the shirt he was watching being removed from his cyber vixen. The look on his face is priceless. Very funny.