assmotorboating 

When an individual places their face between the buttcheeks of another individual. The penetrator then proceeds to stick out their tongue and violently shake their head back and forth. During this exertion the penetratee clenches their buttcheeks and presses the second person's face in between them.

Marc used his giant buttcheeks to engulf Michael's face for an unforgetable assmotorboating.

assmotorboating by gaysasquatch December 3, 2010

Ass Motorboating 

Verb. The act of violently shaking your face in between the cheeks of an amazing ass.

While I was coming out of that pool, I couldn't help but ass motorboating that big ass booty!

Ass Motorboating by Fat Ghandi January 2, 2012