Flasher German car's inside (7)
I believe the answer is:
gaudier
'flasher' is the definition.
('gaudy' can be a synonym of 'flash')
'german car's inside' is the wordplay.
'german' becomes 'ger' (abbreviation).
'car' becomes 'audi' (audi is a german car brand).
'inside' means one lot of letters goes inside another.
'ger' placed around 'audi' is 'GAUDIER'.
(Other definitions for gaudier that I've seen before include "More 4" , "More tastelessly showy" , "More coarsely and brightly coloured" .)