It's just a piece of verbal nonsense which has evolved over the years, a phrase which can be substituted when you can't just think of the right word, or even verb. The Irish use the word 'yolk', as in "Just pass me that yolk ..." or even "Yolk the yolk would you?" - the respondent is supposed to interperet what is meant, and act accordingly, or risk one of the rich vein of insults in the Irish dialict - being an 'idle ginnet' is favourite!