A person, normally a girl, who is so boot ugly that she carries what looks to be a horses mouth on her face.
Damn she gots a horse mouth
She's a real horse mouth
The village bicycle has a real horsey mouth
An girl suffering from the affliction of coming from the English middle or upper classes. Typical characteristics include a reduced lower jaw and enough teeth to fill two normal mouths. Sufferers may also show signs of such diseases as "Being a Sociology Student".
Christ, someone get the sugar cubes, the horse mouth's braying again.
She was no bad till she smiled and her bottom jaw fucked off.. shame. Horse moothed tae fuck.