A slang term used to describe the anus, asshole, or rectum.
Named as such due to the obvious resemblance it bears to a human eye of brown colour; not the eyeball but the specifically the brown iris and the pupil.
"Show us your brown-eye!" Daniel slurred to the girl in a way that seemed to emphasise his immaturity and lack of any intelligence.
Derived from a look that might be given by Gordon Brown (prime minister of England). Gordon has only one eye and is frequently called a one-eyed Scotch cunt.