Top definition
the condition of having an unhygienic mouth due to using your mouth to clean or pleasure ones own or other's lower regions (Down Under). Generally the Down Under Region would refer to feet or genitals or the floor. For a more specific phrase related to post-Cunnilingus mouth effect see: 'Mariana Trench mouth'
"Brush your teeth before you kiss me; you have Australia mouth." or "I'd like to give Margot Robbie Australia mouth."
by Willikin November 01, 2017
Happy St. Patties Day!