'Fuck off big,' can be used in place of 'large,' 'massive,' fucking huge,' and 'gigantic.'
Adds extra 'punch' to a sentence.
Also: 'Fuck off long,' 'Fuck off expensive,' etc.
'Mate, that is a fuck off big hill, and we have to walk up it!'
'I almost got killed by a fuck off big log truck up the lakes!'
Fred: 'Lets cross that river man.'
Bill: 'Nah, that is a fuck off long way, surely we will drown.'