A typically Northern Irish expression also spoken as "face as long as a Lurgan spade" meaning to look miserable or long faced.
One theory about the origin of this expression is that a “Lurgan spade” was an under-paid workman digging what is now the Lurgan Park lake. Another theory is that it is a translation from the Irish language lorga spád meaning the shaft/shin of a spade.
Upon observation you would say...
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!]