To place one's face between another's breasts while moving one's head in a side-to-side motion.

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

The motor boat is done on a girl's clitoris,(putting your lips together and blowing air through them) making a motor boat soundlike a raspberry or zerbert. a lot more fun than in between the tits for both people.

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.

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.

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.