At first you decided awful outfit turned up is flattering one (5)
I believe the answer is:
toady
'flattering one' is the definition.
(sycophantic or flattering person)
'at first you decided awful outfit turned up' is the wordplay.
'at first' indicates taking the first letters.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
The first letters of 'you decided awful outfit turned' is 'ydaot'.
'ydaot' in reverse letter order is 'TOADY'.
'is' is the link.
(Other definitions for toady that I've seen before include "Yes-man" , "Curry favour" , "fawn" , "crawler" , "Person who flatters and behaves obsequiously to another" .)