A or type mouth that smells of what is known as, ass. Butt Mouth can most certainly be a way of describing an animal, such as a dachshund, who by any means, licks its own ass hole, therefore giving off a disturbingly disgusting smelly breath which is best described as, butt.
That nasty wiener dog has the shittiest butt mouth!
by Dr. Buttikiss Maximus January 28, 2012
Any one that of or therefor who has, will, or is eating that of an butthole.
Tommy, i told you not eat my asshole out you buttmouth
by jermey September 18, 2003