A girl with a very sexy body but an unattractive face... This phrase is generally uttered by men who examine the posterior of a lady as they drive by, On the approach they say "Oooohhh" and if her face does not match the beauty of her posterior as they pass they will say "Naaaaaa", hence Una.
I will gladly pay you Tuesday if you will contribute to the cost of my next alcoholic beverage [usually all of the cost of it, and then they sit down next to you, happy days!]