Absolutely nothing about fashion — wearing Japanese sock! (3,1,3)
I believe the answer is:
not a bit
'absolutely nothing' is the definition.
(nothing)
'about fashion wearing japanese sock' is the wordplay.
'about' says the letters should be written in reverse.
'fashion' becomes 'ton' (term for style or fashion).
'wearing' means one lot of letters goes inside another.
'japanese sock' becomes 'tabi' (type of Japanese sock).
'ton' backwards is 'not'.
'not' placed around 'tabi' is 'NOT A BIT'.
(Other definitions for not a bit that I've seen before include "None" , "In no way - far from it" , "In to bat (anag)" .)