Bum-must
The smell of one's anus. Often relating to a mold/mildew infested mobile home must. The musty smell of sweat and gas that is passed by an individual.
Rex: Damn, that fart reeked of Bum-must!
Shawn: Yup, I worked hard on not cleaning by butt for a week
Shawn: Yup, I worked hard on not cleaning by butt for a week