It's a slang Cork pronoun. Cork is a place in Ireland where they all talk incomprehensibly, and anyone from the rest of the country just nods, smiles and backs away.
"A'right boyo, didja see the langer o'er there like?"
=
Hello there you, did you see that nasty person over there?
I've recently read 'Angela's Ashes' a autobiography or memoir written by Frank McCourt and Irish author. Within said book is a sex scene in which Frank takes off all his clothes and gets and erection, his partner looks at him and says "Lord, you might be a scrawny bit of a fellow but that's a fine boyo you have there". This leads me to believe that in the 1930's in Ireland, more specifically Limerick Boyo was a slang term for a penis.
1. Noun. Boyo is slang for boy or lad or mate. Used mostly by English, Irish and Welsh males. (Maybe by the Scottish as well; but who can understand what those cunts are saying?) In the plural format, boyos can refer to a woman's breasts, especially if they are of immodest size.
You're some boyo, ya cunt ya, pissin' all over that poor girl's closet.
Boy oh boy oh boy. Check out the boyos on yer one over there. A man could sprain a wrist.