Its a duck joke my grandad used to tell which was very similar to the song, but he told it to me when I was little.
Basically a duck keeps walking into a pub and going up to the barman and asking if he had any grapes
He did it every day for two weeks
One time the duck came in and the barman said "if you ask if I have any grapes im going to nail your bill to the bar"
The duck goes "got any nails"
The barman says "no"
The duck then says "got any grapes"