1. someone who smells bad
2. an ugly person (used of people to whom your attention has been drawn by a friend, perversely as a potential mate.)
3. someone who has very recently been drunk. Cognate of rat-arsed.
NB: This description should not be used to describe someone as drunk, as you will probably be drunk yourself.
4. someone generally distasteful
This word is widely used in the North of England and Scotland.
"No I don't fancy him, he's a complete minger!"
"You minger! You were completely rat-arsed last night!"
"Bouche and his cronies are complete mingers!"
God she's the worst damn minger I've ever seen!