Flashy style, one's suit to a T! (12)
I believe the answer is:
ostentatious
'flashy' is the definition.
(I know that flashy can be written as ostentatious)
'style one's suit to a t' is the wordplay.
'style' indicates an anagram (style can mean to shape or design).
'ones'+'suit'+'to'+'a'+'t'='onessuittoat'
'onessuittoat' anagrammed gives 'OSTENTATIOUS'.
(Other definitions for ostentatious that I've seen before include "Showy and vulgar" , "Flamboyant" , "Designed to impress" , "Pretentious, showy" , "Given to pretentious display" .)