O boy! Mink's fantastic for me (2,2,4)
I believe the answer is:
in my book
'for me' is the definition.
(in my opinion)
'o boy mink's fantastic' is the wordplay.
'fantastic' is an anagram indicator.
'o'+'boy'+'mink'='oboymink'
'oboymink' is an anagram of 'IN MY BOOK'.
(Other definitions for in my book that I've seen before include "How to describe writer's published words" , "place for autobiographical details" , "as far as I'm concerned?" , "As I see it" , "To my way of thinking" .)