Butt-tang
(Noun) The bitter taste and/or flavor that can be found on both the tongue of a person who has just given someone anilingus as well on/in the asshole of the person who has just received the anilingus. The undesirable taste is the direct result of the slovenly, unwashed receiver not making any effort whatsoever at personal hygiene, specifically washing their nasty ass.
James tried to somehow put the horrible and pungent taste of butt-tang from his mouth but he was not being very successful at it. He barely recalled licking Betsy's asshole in a night of drunken and horny revelry. At times he ran to the to the restroom on the verge of vomiting. 'That nasty-ass bitch' he thought.