A Doonie is a Vagina... Term was Popularized by YNLouie & YN Jay. In songs they mention "beating peoples doonies down" which is the verbal phrase for Doonies. which means the same as beating up a pussy or fuckung the shit outta someone.
Doonies-reference to a male beating a females pussy so hard it causes vibration in her organs causing them to move downwards hence the reference I beat her doonies down