Vain politician yet to be ruffled outside (5)
I believe the answer is:
empty
'vain' is the definition.
(I've seen this before)
'politician yet to be ruffled outside' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'to be ruffled' indicates anagramming the letters.
'outside' means one lot of letters goes inside another.
'yet' with letters rearranged gives 'ety'.
'mp' going inside 'ety' is 'EMPTY'.
(Other definitions for empty that I've seen before include "Dead man" , "Unfilled" , "left for the milkman?" , "Arabic quarter" , "Evacuate" .)