A humorous traditional Irish song based on an older ballad, 'Our Goodman' (Child Ballad #274), sometimes called '4 Nights Drunk'. Usually only 5 of the 7 nights are sung because of the randy nature of the final 2 (you'll hear what we mean).
Each night is a verse, followed by a chorus, in which a man comes home in a drunken state to find evidence of another man having been with his wife, which she explains away, not entirely convincingly.
The Child Ballads are a collection of 305 ballads from England and Scotland, and their American variants, collected by Francis James Child in the late 19th century. The collection was published as The English and Scottish Popular Ballads between 1882 and 1898.
Verses very each time it is sung and often depending on the audience reaction as the song is performed