One boasts retro attire with good design (8)
I believe the answer is:
braggart
'one boasts' is the definition.
(I've seen this before)
'retro attire with good design' is the wordplay.
'retro' says the letters should be written in reverse (retro is Latin for 'backwards').
'attire' becomes 'garb' (both can mean clothing).
'with' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'design' becomes 'art' (design is an art).
'garb' backwards is 'brag'.
'brag'+'g'+'art'='BRAGGART'
(Other definitions for braggart that I've seen before include "bigmouth" , "Boastful type" , "Big noter" , "Show-off" , "Boastful person" .)