Someone eating or aquiring comically large and/or frequent amounts of food, or appearing to do so.
Must be said with a south-west english accent (Cornwall, Devon, etc.)
Only works with the 'You' at the front, and only happens with 'You' and 'Bif' on one note, and 'fat'and 'fer' on a higher one.
There's no real emphasis anywhere, and it's deadpan despite the humourous intent.