One in front gets conceited (4)
I believe the answer is:
vain
'conceited' is the definition.
('vain' can be a synonym of 'conceited')
'one in front' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'front' becomes 'van' (I've seen this before).
'i' going inside 'van' is 'VAIN'.
'gets' acts as a link.
(Other definitions for vain that I've seen before include "It's no good" , "Conceited, self-important" , "Conceited or unsuccessful" , "without success" , "Conceited, arrogant" .)