a motorboat involves a girl with breasts large enough for a human head to fit between them. The owner of the head then proceeds to blow out of their mouth vibrating their lips. This action will make a sound very similar to a motorboat engine, hence the name.

The act of placing ones head between breasts and doing a "raspberry".

Refers to a lady with ample breasts, or ample everything, whose physique built to perform a motorboat would be an easy task. The motorboating may be done anywhere on the corpus where one can press the face in between any skinfolds, 'as long as the cheeks are warmed'.

When you go up to a girl and stick your head in there tits and go burrrrrr, than move your head side to side

specifically for brass players in an orchestra: When they don't use enough air and a motorboat like sound comes out

Mainly a sex act performed as a favour to men who drive convertible drop top coupés by women who want to get a ride with the top down. The man rolls down the hard top roof of the car and proceeds to place his mouth and nose in between the woman´s exposed breasts, while rocking his head side to side very rapidly while making a , lip-vibrating "brrr" sound. The vibrations stimulates the nerves around the nipples making them rock hard and is usually an invitation for the woman to straddle him for sex inside the car.

While performing oral sex on a girl, flap your lips together on her clit, thus imitating the sound of a motorboat. She'll love you forever.