derfin biscuit

An accusatory phrase that implies that something you just heard is made up, imagined or a far reaching fantasy.

Some biscuits resemble the shape of a cow patty so this is a clean way of saying "bullshit" or "BS".

That is a total derfin biscuit...you just made that up!
Nobody would believe that in that "derfin biscuit".
That's some derfin BS right there!