backwards motorboat 

The act of placing one's face in the butt crack of another person, followed by rigorous side-to-side motion of the head accompanied by the vibrating of the lips causing a sound similar to an outboard motor. See Motorboating

Do know if he can backwards motorboat himself?

No, I've been doing it for him for the past few months. He's just not that flexible anymore.

backwards motorboat by 'ice' June 8, 2009